Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (46,239)	$ (50,641)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	522	311
Loss on disposal of property and equipment		21
Stock-based compensation expense	10,307	6,478
Amortization of debt issuance costs	658	335
Amortization of premium/discount on investments	125	499
Change in fair value of foreign currency derivative	1,858	7,372
Changes in operating assets and liabilities:
Receivables	(217)	275
Inventory	500	(620)
Prepaid expenses and other assets	17	667
Deferred collaboration expense	51	43
Accounts payable and accrued expenses	1,303	(12,066)
Interest payable	1,715	817
Deferred revenue	(1,224)	(1,075)
Net cash used in operating activities	(30,624)	(47,584)
Investing activities
Acquisitions of property and equipment	(213)	(5,278)
Change in restricted cash	(1,576)	106
Purchases of investments	(39,572)
Sales and maturities of investments	32,527	38,272
Net cash (used in) provided by investing activities	(8,834)	33,100
Financing activities
Sale of common stock, net	133,500
Net proceeds from common stock issued under stock-based compensation plans	1,491	204
Proceeds from senior credit facility		22,658
Payment of foreign currency derivative collateral		(2,190)
Increase in lease financing obligation	139	300
Net cash provided by financing activities	135,130	20,972
Increase in cash and cash equivalents	95,672	6,488
Cash and cash equivalents at beginning of period	22,104	28,899
Cash and cash equivalents at end of period	$ 117,776	$ 35,387