Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net loss	$ (27,712)	$ (38,624)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	7,416	4,303
Depreciation and amortization	1,441	1,213
Payment of accrued interest on long-term debt	0	(2,593)
Loss on extinguishment of long-term debt	0	7,143
Amortization of debt discount and deferred financing costs	355	819
Loss on equity securities	0	(1,360)
Amortization (accretion) of discount or premium on short-term investments	31	(141)
Non-cash operating lease expense	838	775
Provision for inventory obsolescence and bad debts	951	14
Changes in operating assets and liabilities:
Accounts receivable	(2,462)	5,926
Inventory	(2,159)	(2,712)
Prepaid expenses and other assets	(3,559)	3,318
Accounts payable	943	(260)
Accrued liabilities	(1,060)	(426)
Accrued compensation and other employee benefits	(3,774)	(5,821)
Customer deposits	(299)	(2,305)
Deferred revenue	1,244	1,115
Operating lease liabilities	(1,050)	(887)
Net cash used in operating activities	(28,856)	(27,783)
Investing activities
Purchases of property and equipment	(2,672)	(3,939)
Proceeds from sale of short-term investments	0	4,000
Proceeds from maturity of short-term investments	15,362	48,584
Purchases of short-term investments	0	(38,804)
Net cash provided by investing activities	12,690	9,841
Financing activities
Proceeds from issuance of 2025 convertible senior notes and borrowings under long-term debt agreement	0	230,000
Fees paid for issuance of 2025 convertible senior notes and long-term debt borrowings	0	(7,403)
Repayment of long-term debt	0	(80,000)
Fees paid upon extinguishment of debt	0	(4,845)
Proceeds from issuance of common stock warrants	0	737
Tax withholdings related to net share settlements of restricted stock units	(2,585)	(2,006)
Proceeds from issuance of common stock for employee stock purchase plan	1,192	1,122
Proceeds from exercise of stock options	2,249	6,969
Net cash provided by financing activities	856	144,574
Net increase (decrease) in cash and cash equivalents	(15,310)	126,632
Effect of exchange rate changes on cash and cash equivalents	146	(73)
Cash and cash equivalents
Beginning of period	411,666	29,033
End of period	$ 396,502	$ 155,592