Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (65,757)	$ (41,935)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	8,094	7,958
Depreciation and amortization	2,814	2,377
Payment of accrued interest of long-term debt	(2,593)	0
Loss on extinguishment of long-term debt	7,143	0
Amortization of debt discount and deferred financing costs	3,454	343
Loss on equity securities	300	0
Amortization of premium (discount) on short-term investments	(150)	236
Non-cash operating lease expense	1,596	1,332
Conversion of accrued interest to long-term debt	0	941
Provision for inventory obsolescence and bad debts	14	592
Changes in operating assets and liabilities:
Accounts receivable	5,129	(1,752)
Inventory	(6,559)	(4,361)
Prepaid expenses and other assets	5,493	(3,488)
Accounts payable	(2,835)	(2,551)
Accrued liabilities	47	(200)
Accrued compensation and other employee benefits	(3,117)	(2,306)
Customer deposits	(3,100)	(798)
Deferred revenue	1,075	(4,624)
Operating lease liabilities	(1,187)	(920)
Net cash used in operating activities	(50,139)	(49,156)
Investing activities
Purchases of property and equipment	(5,365)	(1,147)
Proceeds from sale of short-term investments	17,218	0
Proceeds from maturity of short-term investments	69,284	60,120
Purchases of short-term investments	(38,804)	(102,579)
Net cash provided by (used in) investing activities	42,333	(43,606)
Financing activities
Proceeds from issuance of 2025 convertible senior notes	230,000	20,000
Fees paid for issuance of 2025 convertible senior notes	(7,403)	(100)
Repayment of long-term debt	(80,000)	0
Fees paid upon extinguishment of debt	(4,845)	0
Proceeds from sale of common stock, net	0	68,273
Proceeds from issuance of common stock warrants	737	1,306
Tax withholdings related to net share settlements of restricted stock units	(2,006)	(1,299)
Proceeds from issuance of common stock for employee stock purchase plan	1,122	939
Proceeds from exercise of stock options	9,641	12,665
Net cash provided by financing activities	147,246	101,784
Net increase in cash and cash equivalents	139,440	9,022
Effect of exchange rate changes on cash and cash equivalents	(30)	(7)
Cash and cash equivalents
Beginning of period	29,033	24,356
End of period	168,443	33,371
Operating lease right-of-use assets obtained in exchange for lease obligations	$ 449	$ 27,880