Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (68,683)	$ (44,223)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	357	377
Stock-based compensation expense	8,702	4,987
Amortization of debt issuance costs	596	455
Amortization of premium/discount on investments	(17)	140
Change in fair value of foreign currency derivative	646	1,185
Changes in operating assets and liabilities:
Receivables	691	3,775
Inventory	649	(221)
Prepaid expenses and other assets	84	(347)
Deferred collaboration expense		140
Accounts payable and accrued expenses	2,579	4,447
Interest payable	2,897	2,737
Deferred revenue		(7,000)
Net cash used in operating activities	(51,499)	(33,548)
Investing activities
Acquisitions of property and equipment	(180)	(221)
Purchases of investments	(3,018)	(16,754)
Sales and maturities of investments	41,357	34,435
Net cash provided by investing activities	38,159	17,460
Financing activities
Payment of senior credit facility		(3,450)
Proceeds from senior credit facility	19,477
Net proceeds from common stock issued under stock-based compensation plans	977	736
Increase in lease financing obligation		(37)
Net cash provided by (used in) financing activities	20,454	(2,751)
Increase (decrease) in cash, cash equivalents and restricted cash	7,114	(18,839)
Cash, cash equivalents and restricted cash at beginning of period	28,275	53,568
Cash, cash equivalents and restricted cash at end of period	$ 35,389	$ 34,729