Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (44,815)	$ (76,369)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,811	1,853
Stock-based compensation	7,177	5,972
Amortization of debt issuance costs	708	592
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	344	419
Increase in inventory	403	(194)
(Increase) decrease in prepaid expenses and other current assets	(3,957)	481
Decrease in other assets	186	0
Decrease in accounts payable and other liabilities	(13,842)	(6,844)
Decrease in deferred revenue	(535)	(25,208)
Net cash used in operating activities	(52,520)	(99,298)
Cash flows from investing activities:
Purchases of property and equipment	(70)	(55)
Purchases of investments	(106,706)	(49,638)
Maturities of investments	91,600	104,123
Net cash provided by investing activities	(15,176)	54,430
Cash flows from financing activities:
Proceeds from issuance of common stock	0	392
Repurchase of common stock	(941)	(972)
Repayment of debt borrowings, net of fees	(643)	(1,169)
Net cash (used in) provided by financing activities	(1,584)	(1,749)
Net increase (decrease) in cash and cash equivalents	(69,280)	(46,617)
Cash and cash equivalents at beginning of period	80,386	61,661
Cash and cash equivalents at end of period	11,106	15,044
Supplemental disclosure of cash flow information:
Cash paid for interest	9,610	6,726
Supplemental disclosure of non-cash investing and financing activities:
Unrealized gain on investments	$ 98	$ 4