Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (19,718)	$ (36,230)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,086	879
Stock-based compensation expense	2,261	1,778
Amortization of debt discount	256	257
Loss on disposal of assets and impairment charges	173
Deferred income taxes	48	486
Changes in operating assets and liabilities:
Receivables, net	(34,728)	(7,624)
Prepaid expenses and other assets	3,748	(11,911)
Inventories	(3,101)	3,596
Accounts payable and accrued expenses	4,430	15,798
Net cash used in operating activities	(45,545)	(32,971)
Cash flows from investing activities:
Purchase of property and equipment	(1,736)	(918)
Payments for licenses	(64)	(4,175)
Purchases of short-term investments	(23,571)
Sales and maturities of short-term investments	14,920	57,291
Net cash (used in) provided by investing activities	(10,451)	52,198
Cash flows from financing activities:
Proceeds from issuance of debt	435	743
Proceeds from exercise of stock options	344	278
Repayment of finance lease obligations and long-term debt	(47)	(45)
Net cash provided by financing activities	732	976
Net (decrease) increase in cash and cash equivalents	(55,264)	20,203
Cash and cash equivalents, beginning of period	127,674	49,794
Effect of exchange rate changes on cash and cash equivalents	(427)	1,006
Cash and cash equivalents, end of period	71,983	71,003
Supplemental cash flow disclosures
Interest paid	1,390	981
Non-cash investing and financing activities:
Accrued purchases of property and equipment	1,009	634
Accrued purchases of licenses	500
ROU assets derecognized from modification of operating lease obligations	(468)
ROU assets recognized in exchange for operating lease obligations	$ 353	$ 583