Condensed 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	$ (41,538)	$ (41,569)
Adjustments to reconcile net loss to cash used in operating activities
Depreciation	219	563
Amortization of right-of-use assets	263
Stock-based compensation expense	3,853	3,657
Accretion of discount on marketable securities	(431)	(230)
Amortization of debt discount and debt issuance costs	2,069	1,884
Premium paid on securities purchased		(3)
Changes in operating assets and liabilities:
Accounts receivable	(2,009)	(1,987)
Inventory	(2,326)	(726)
Prepaid expenses, other current and long-term assets	844	(620)
Accounts payable	(348)	(2,806)
Accrued expenses and other current liabilities	1,665	(3,144)
Lease liabilities and other long-term liabilities	(242)
Net cash used in operating activities	(37,981)	(44,981)
Cash flows from investing activities
Purchases of property and equipment	(1,068)	(334)
Purchases of marketable securities	(76,308)	(32,546)
Sale and redemption of marketable securities	118,563	99,462
Net cash provided by investing activities	41,187	66,582
Cash flows from financing activities
Payments on notes payable	(2,500)	(2,500)
Proceeds from the exercise of stock options		414
Net cash used in by financing activities	(2,500)	(2,086)
Net increase in cash, cash equivalents, and restricted cash	706	19,515
Cash, cash equivalents, and restricted cash at beginning of period	87,229	128,389
Cash, cash equivalents, and restricted cash at end of period	87,935	147,904
Non-cash investing and financing activities
Right-of-use asset obtained in exchange for operating lease obligation	6,595
Purchases of property and equipment in accounts payable and accrued expenses		13
Supplemental disclosures of cash flow information
Cash paid for interest	$ 170	$ 326