Condensed 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	$ (78,025)	$ (85,444)
Adjustments to reconcile net loss to cash used in operating activities
Depreciation	435	1,069
Amortization of right-of-use assets	553
Stock-based compensation expense	8,070	7,641
Accretion of discount on marketable securities	(836)	(461)
Amortization of debt discount and debt issuance costs	4,184	3,811
Premium paid on securities purchased	(26)	(4)
Changes in operating assets and liabilities:
Accounts receivable	(9,468)	(4,650)
Inventory	(4,512)	(1,505)
Prepaid expenses, other current and long-term assets	1,287	429
Accounts payable	(271)	(629)
Accrued expenses and other current liabilities	787	(2,283)
Lease liabilities and other long-term liabilities	(541)
Net cash used in operating activities	(78,363)	(82,026)
Cash flows from investing activities
Purchases of property and equipment	(1,068)	(561)
Purchases of marketable securities	(96,198)	(65,215)
Sale and redemption of marketable securities	138,061	196,072
Net cash provided by investing activities	40,795	130,296
Cash flows from financing activities
Payments on notes payable	(5,000)	(5,000)
Proceeds from the exercise of stock options		1,777
Proceeds from employee stock purchase plan	1,040	1,129
Net cash used in by financing activities	(3,960)	(2,094)
Net (decrease) increase in cash, cash equivalents, and restricted cash	(41,528)	46,176
Cash, cash equivalents, and restricted cash at beginning of period	87,229	128,389
Cash, cash equivalents, and restricted cash at end of period	45,701	174,565
Non-cash investing and financing activities
Right-of-use asset obtained in exchange for operating lease obligation	7,046
Purchases of property and equipment in accounts payable and accrued expenses		79
Supplemental disclosures of cash flow information
Cash paid for interest	$ 3,699	$ 4,015