Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (116,257)	$ (129,084)
Adjustments to reconcile net loss to cash used in operating activities
Depreciation	733	1,494
Amortization of right-of-use assets	942
Stock-based compensation expense	12,095	11,640
Non cash interest expense	459
Accretion of discount on marketable securities	(1,155)	(803)
Loss from debt extinguishment	352
Amortization of debt discount and debt issuance costs	6,505	5,786
Premium paid on securities purchased	(27)	(215)
Changes in operating assets and liabilities:
Accounts receivable	(16,195)	(8,388)
Inventory	(6,151)	(3,044)
Prepaid expenses, other current and long-term assets	265	(1,273)
Accounts payable	(576)	2,300
Accrued expenses and other current liabilities	10,033	3,826
Lease liabilities and other long-term liabilities	(839)
Net cash used in operating activities	(109,816)	(117,761)
Cash flows from investing activities
Purchases of property and equipment	(1,118)	(688)
Purchases of marketable securities	(106,105)	(157,116)
Sale and redemption of marketable securities	191,059	269,417
Net cash provided by investing activities	83,836	111,613
Cash flows from financing activities
Proceeds from borrowings under term loan	40,000
Payment of debt issuance costs	(161)
Payments on notes payable	(14,367)	(7,500)
Proceeds from the exercise of stock options	8	1,896
Proceeds from employee stock purchase plan	1,040	1,129
Net cash provided by (used in) financing activities	26,520	(4,475)
Net increase (decrease) in cash, cash equivalents, and restricted cash	540	(10,623)
Cash, cash equivalents, and restricted cash at beginning of period	87,229	128,389
Cash, cash equivalents, and restricted cash at end of period	87,769	117,766
Non-cash investing and financing activities
Right-of-use asset obtained in exchange for operating lease obligation	9,560
Purchases of property and equipment in accounts payable and accrued expenses	1,410	143
Supplemental disclosures of cash flow information
Cash paid for interest	$ 3,991	$ 4,268