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Expected Term Measurement Input, Expected Term [Member] Antidilutive Securities, Name Antidilutive Securities, Name [Domain] Other Other Operating Activities, Cash Flow Statement Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Accrued expenses Increase (Decrease) in Accrued Liabilities Debt instrument, additional principal amount Debt Instrument, Over-Allotment Option, Amount Debt Instrument, Additional Face Amount Adjustments to reconcile net loss to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Series A warrants Common Stock Warrant Expiring October 2022 Common Stock Warrant Expiring October 2022 [Member] Common Stock Warrant Expiring October 2022 Unrealized gain (loss) on short-term investments Unrealized gain (loss) on short-term investments Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Loss before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Research and development Research and Development Expense Cash equivalents Cash Equivalents [Member] Reclassification Reclassification, Comparability Adjustment [Policy Text Block] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Increase in denominator shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Document Period End Date Document Period End Date Contractual interest expense Interest Expense, Debt, Excluding Amortization Employee-related liabilities Increase (Decrease) in Employee Related Liabilities Entity Registrant Name Entity Registrant Name Income Statement [Abstract] Income Statement [Abstract] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Operating lease liabilities - long-term Operating lease liabilities - long-term Operating Lease, Liability, Noncurrent Prepaid and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Schedule of Estimated Fair Value of Short-Term Investments Cash, Cash Equivalents and Investments [Table Text Block] Deferred rent—long-term Deferred Rent Credit, Noncurrent Purchase of capped call options related to convertible notes Capped call transactions net cost Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments Conversion Instance, 130% Conversion Instance, 130% [Member] Conversion Instance, 130% [Member] Unamortized debt discount and debt issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Organization And Basis Of Presentation [Table] Organization And Basis Of Presentation [Table] Organization and basis of presentation. 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Gross Unrealized Loss Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax High Bluff Drive, San Diego, California High Bluff Drive, San Diego, California [Member] High Bluff Drive, San Diego, California [Member] Sale of Stock Sale of Stock [Axis] Foreign currency translation gain (loss) Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Schedule of Assumptions Used to Estimate Fair Values of Common Stock Warrants Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Outstanding warrants (in shares) Class of Warrant or Right, Outstanding Warrants to purchase common stock Common stock warrants Shares underlying outstanding warrants Warrant [Member] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Class of Warrant or Right [Table] Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Axis] Principal Debt Instrument, Face Amount Level 2 (Level 2) Fair Value, Inputs, Level 2 [Member] Vesting Vesting [Axis] Offering period Offering Period Offering period. Equity [Abstract] Equity [Abstract] Total assets Assets, Fair Value Disclosure Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Entity Central Index Key Entity Central Index Key Deferred revenue Deferred revenue Contract with Customer, Liability, Current Entity Emerging Growth Company Entity Emerging Growth Company Accounting Standards Update [Extensible List] Accounting Standards Update [Extensible List] Decreases in warranty estimates Standard and Extended Product Warranty Accrual, Increase (Decrease) for Preexisting Warranties Cumulative Effect, Period of Adoption Cumulative Effect, Period of Adoption [Axis] Conversion price (usd per share) Debt Instrument, Convertible, Conversion Price Weighted average shares used to compute diluted net loss per share (in shares) Weighted Average Number of Shares Outstanding, Diluted Net loss per share, basic (usd per share) Earnings Per Share, Basic Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Number of operating segments Number of Operating Segments Debt Disclosure [Abstract] Debt Disclosure [Abstract] Other Current Liabilities Other Current Liabilities [Member] Weighted-average remaining lease term (in years) Operating Lease, Weighted Average Remaining Lease Term Thereafter Lessee, Operating Lease, Liability, To Be Paid, After Year Four Lessee, Operating Lease, Liability, To Be Paid, After Year Four Accounts Receivable And Inventories Disclosure [Abstract] Accounts Receivable And Inventories Disclosure [Abstract] Accounts Receivable And Inventories Disclosure [Abstract] Amortization of debt discount and debt issuance costs Amortization of Debt Issuance Costs and Discounts Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Cash equivalents maturity term Cash Equivalents Maturity Term Cash equivalents maturity term. Compensation cost Share-based Payment Arrangement, Expense Balance Sheet Location Balance Sheet Location [Axis] Issuance of common stock for Employee Stock Purchase Plan Stock Issued During Period, Value, Employee Stock Purchase Plan Common stock, $0.001 par value; 200,000 shares authorized, 62,116 and 59,396 shares issued and outstanding at September 30, 2020 (unaudited) and December 31, 2019, respectively. 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Supplemental schedule of non-cash investing and financing activities Noncash Investing and Financing Items [Abstract] Insulin Pump Insulin Pump [Member] Insulin pump. Exercise of stock options (in shares) Common stock shares issued upon option exercises (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Net increase in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Schedule of Future Minimum Payments Under Non-cancellable Operating Leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Options to purchase common stock Stock Options Share-based Payment Arrangement, Option [Member] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Weighted average shares used to compute basic net loss per share (in shares) Weighted Average Number of Shares Outstanding, Basic Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Sale of Stock Sale of Stock [Domain] Plan Name Plan Name [Domain] Other current liabilities Increase (Decrease) in Other Current Liabilities Organization and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Right-of-use assets obtained in exchange for operating lease obligations Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Number of legal proceedings, regulatory matters, or other, disputes or claims Number Of Legal Proceedings Regulatory Matters Or Other Disputes Or Claims Number of legal proceedings, regulatory matters, or other, disputes or claims. Convertible senior notes, fair value Long-term Debt, Fair Value Income tax expense (benefit) Income tax expense Income Tax Expense (Benefit) Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Total liabilities Financial and Nonfinancial Liabilities, Fair Value Disclosure Accrued expenses Accrued Liabilities, Current Net loss per share, diluted (usd per share) Earnings Per Share, Diluted Cumulative Effect, Period of Adoption Cumulative Effect, Period of Adoption [Domain] First anniversary Share-based Payment Arrangement, Tranche One [Member] Assumptions used to estimate fair value of common stock warrants Warrants and Rights Outstanding, Measurement Input Schedule of Changes in Fair Value of Total Level 3 Financial Assets Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Total Contract with Customer, Liability Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Debt instrument, convertible, threshold trading days consecutive trading days Debt Instrument, Convertible, Threshold Consecutive Trading Days Benefit for deferred income taxes Deferred Income Tax Expense (Benefit) Number of insulin pumps Number Of Insulin Pumps Number Of Insulin Pumps Award Type Award Type [Axis] Secondary Public Offering Secondary Public Offering [Member] Secondary public offering. Lease Contractual Term [Domain] Lease Contractual Term [Domain] Amortization of debt discount Amortization of Debt Issuance Costs Maximum Maximum [Member] Security Exchange Name Security Exchange Name Purchases of short-term investments Payments to Acquire Short-term Investments Accumulated Deficit Retained Earnings [Member] Schedule of Interest Expense Recognized Interest Income and Interest Expense Disclosure [Table Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Less: allowance for credit losses Balance at beginning of the period Balance at end of the period Accounts Receivable, Allowance for Credit Loss Common stock warrants Warrants and Rights Outstanding Equity Award Award Type [Domain] Investments Investments [Domain] Document Transition Report Document Transition Report Corporate debt securities Corporate debt securities Corporate Debt Securities [Member] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Current liabilities: Liabilities, Current [Abstract] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value, Measurements, Recurring Fair Value, Recurring [Member] Allowance for product returns Allowance For Sales Returns Allowance for sales returns. Segment Reporting Segment Reporting, Policy [Policy Text Block] Schedule of Shares of Common Stock Reserved for Future Issuance Schedule Of Common Stock Reserved For Future Issuance [Table Text Block] Schedule of common stock reserved for future issuance. Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Short-term investments Short-term Investments