Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (106,275)	$ (73,820)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	539	572
Stock-based compensation expense	14,031	7,072
Amortization of debt issuance costs	936	676
Amortization of premium/discount on investments	1	152
Change in fair value of foreign currency derivative	532	606
Changes in operating assets and liabilities:
Receivables	695	2,723
Inventory	(127)	(821)
Prepaid expenses and other assets	(1,018)	(1,063)
Deferred collaboration expense		144
Accounts payable and accrued expenses	9,975	3,947
Interest payable	1,575	(1,668)
Deferred revenue		(7,100)
Net cash used in operating activities	(79,136)	(68,580)
Investing activities
Acquisitions of property and equipment	(263)	(262)
Purchases of investments	(3,018)	(43,158)
Sales and maturities of investments	64,954	51,355
Net cash provided by investing activities	61,673	7,935
Financing activities
Sale of common stock, net		53,400
Proceeds from senior credit facility	19,477	10,353
Payment of senior credit facility		(4,025)
Net proceeds from common stock issued under stock-based compensation plans	1,161	1,495
Decrease in lease financing obligation		(56)
Net cash provided by financing activities	20,638	61,167
Increase in cash, cash equivalents and restricted cash	3,175	522
Cash, cash equivalents and restricted cash at beginning of period	28,275	53,568
Cash, cash equivalents and restricted cash at end of period	$ 31,450	$ 54,090