Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (38,624)	$ (21,898)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,303	2,882
Depreciation and amortization	1,213	1,177
Payment of accrued interest of long-term debt	(2,593)	0
Loss on extinguishment of long-term debt	7,143	0
Amortization of deferred financing costs	819	163
Loss on equity securities	1,360	0
Amortization of premium on short-term investments	(141)	(6)
Non-cash operating lease cost	775	651
Conversion of accrued interest to long-term debt	0	453
Provision for bad debts	6	38
Provision for inventory obsolescence	8	442
Changes in operating assets and liabilities:
Accounts receivable	5,926	(833)
Inventory	(2,712)	(465)
Prepaid expenses and other assets	3,318	(1,377)
Accounts payable	(260)	(1,893)
Accrued liabilities	(426)	1,124
Accrued compensation and other employee benefits	(5,821)	(4,765)
Customer deposits	(2,305)	(2,226)
Deferred revenue	1,115	(833)
Operating lease liabilities	(887)	(811)
Net cash used in operating activities	(27,783)	(28,177)
Investing activities
Purchases of property and equipment	(3,939)	(165)
Proceeds from sale of short-term investments	4,000	0
Proceeds from maturity of short-term investments	48,584	39,520
Purchases of short-term investments	(38,804)	(28,100)
Net cash provided by investing activities	9,841	11,255
Financing activities
Proceeds from issuance of 2025 convertible senior notes	230,000	0
Fees paid for issuance of 2025 convertible senior notes	(7,403)	0
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	697
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	6,969	8,075
Net cash provided by financing activities	144,574	76,685
Net increase in cash and cash equivalents	126,632	59,763
Effect of exchange rate changes on cash and cash equivalents	(73)	(10)
Cash and cash equivalents
Beginning of period	29,033	24,356
End of period	$ 155,592	$ 84,109