Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS USED IN OPERATING ACTIVITIES:
Net loss	$ (132,993)	$ (221,337)	$ (254,237)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,308	2,867	1,951
Amortization of premium (accretion of discount) on marketable securities, net	(394)	(390)	(264)
Impairment loss on operating lease right of use assets	339
Stock-based compensation expense	23,615	28,701	35,003
Amortization of debt discount and issuance costs	15,785	13,800	4,816
Loss on disposals of property and equipment	201	0	0
Changes in operating assets and liabilities:
Inventory	887	(1,844)	(4,366)
Accounts receivables, net	(6,531)	(12,317)	(4,441)
Prepaid expenses	1,711	(8,667)	(3,689)
Other current assets	356	989	(1,362)
Operating lease right of use assets	2,034
Other long-term assets	30	255	(248)
Accounts payable	1,804	311	(2,213)
Accrued expenses and other current liabilities	10,827	(7,000)	22,563
Lease liability, operating leases	(2,298)
Other non-current liabilities	(95)	(94)	(190)
Net cash used in operating activities	(82,414)	(204,726)	(206,677)
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of property and equipment	0	(185)	(2,341)
Payment of milestone related to intangible asset	0	0	(8,712)
Purchases of marketable securities	(119,502)	(499)	(429,296)
Sales and maturities of marketable securities	206,779	135,000	191,363
Net cash (used in) provided by investing activities	87,277	134,316	(248,986)
CASH FLOWS PROVIDED BY FINANCING ACTIVITIES:
Proceeds from exercise of stock options and warrants	3,869	9,106	17,478
Proceeds from issuance of convertible notes	0	0	305,000
Deferred financing costs	0	0	(9,360)
Proceeds from employee stock purchase plan	1,840	2,566	2,550
Net cash provided by financing activities	5,709	11,672	315,668
NET (DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	10,572	(58,738)	(139,995)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH AT BEGINNING OF YEAR	59,881	118,619	258,614
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH AT END OF YEAR	70,453	59,881	118,619
SUPPLEMENTAL DISCLOSURES:
Cash paid for interest	9,150	9,582	0
Property and equipment purchases in accrued expense	0	$ 309	$ 352
Right of use assets obtained in exchange for operating lease liability	$ 9,077