Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities
Net loss	$ (54,732)	$ (65,757)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	15,405	8,094
Depreciation and amortization	2,880	2,814
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	709	3,454
Loss on equity securities	0	300
Accretion of discount on short-term investments	(2,401)	(150)
Non-cash operating lease expense	1,671	1,596
Provision for inventory obsolescence and bad debts	1,369	14
Changes in operating assets and liabilities:
Accounts receivable	(1,191)	5,129
Inventory	(7,048)	(6,559)
Prepaid expenses and other assets	(5,684)	5,493
Accounts payable	6,041	(2,835)
Accrued liabilities	553	47
Accrued compensation and other employee benefits	(806)	(3,117)
Customer deposits	(149)	(3,100)
Deferred revenue	1,306	1,075
Operating lease liabilities	(2,090)	(1,187)
Net cash used in operating activities	(44,167)	(50,139)
Investing activities
Purchases of property and equipment	(3,784)	(5,365)
Proceeds from sale of short-term investments	4,000	17,218
Proceeds from maturity of short-term investments	24,764	69,284
Purchases of short-term investments	(235,263)	(38,804)
Net cash (used in) provided by investing activities	(210,283)	42,333
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	4,503	9,641
Repayment of finance lease obligations	(119)	0
Net cash provided by financing activities	2,991	147,246
Net increase (decrease) in cash and cash equivalents	(251,459)	139,440
Effect of exchange rate changes on cash and cash equivalents	(9)	(30)
Cash and cash equivalents
Beginning of period	411,848	29,033
End of period	160,380	168,443
Supplemental Cash Flow Information [Abstract]
Finance lease right-of-use assets obtained in exchange for lease obligations	$ 192	$ 449