Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (21,797)	$ (41,820)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	901	925
Stock-based compensation	3,411	3,074
Amortization of debt issuance costs	346	307
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	1,534	343
Increase in inventory	74	(164)
(Increase) decrease in prepaid expenses and other current assets	(2,018)	150
Decrease in other assets	91	(3)
Decrease in accounts payable and other liabilities	(8,171)	9,382
Decrease in deferred revenue	9	(18,969)
Net cash used in operating activities	(25,620)	(46,775)
Cash flows from investing activities:
Purchases of property and equipment	(70)	(40)
Purchases of investments	(87,256)	(46,892)
Maturities of investments	79,600	53,995
Net cash provided by investing activities	(7,726)	7,063
Cash flows from financing activities:
Proceeds from issuance of common stock	0	25
Repurchase of common stock	(941)	(972)
Repayment of debt borrowings, net of fees	(321)	(581)
Net cash (used in) provided by financing activities	(1,262)	(1,528)
Net increase (decrease) in cash and cash equivalents	(34,608)	(41,240)
Cash and cash equivalents at beginning of period	80,386	61,661
Cash and cash equivalents at end of period	45,778	20,421
Supplemental disclosure of cash flow information:
Cash paid for interest	3,698	774
Supplemental disclosure of non-cash investing and financing activities:
Unrealized gain on investments	$ 45	$ (172)