Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net loss	$ (4,984)	$ (42,127)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,204	483
Non-cash interest expense	253	268
Non-cash change in fair value of PIPE Warrant liability	(9,660)	24,409
Non-cash charge for settlement warrants (Note 9)	(667)
Amortization of premium and discount on investments	2	12
Changes in operating assets and liabilities:
Accounts receivable	(571)	582
Insurance recovery (Note 9)	15,000
Prepaid expenses and other current assets	319	372
Other noncurrent assets	8	618
Accounts payable	386	1,175
Accrued contract research	(1,330)	2,245
Other accrued liabilities	(774)	(171)
Settlement liability (Note 9)	(15,000)
Deferred revenue	683	(313)
Deferred research and development reimbursements	(471)
Net cash used in operating activities	(15,602)	(12,447)
Investing activities
Purchases of marketable securities	(6,733)	(9,286)
Proceeds from maturities and sales of marketable securities	25,312	8,252
Net cash provided by (used in) investing activities	18,579	(1,034)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	518	21,035
Proceeds from issuance of common stock to related parties		3,210
Proceeds from issuance of stock for stock-based compensation arrangements	185
Proceeds from issuance of loans payable		5,000
Payment of end-of-term debt costs (Note 6)	(540)
Net cash provided by financing activities	163	29,245
Net increase in cash and cash equivalents	3,140	15,764
Cash and cash equivalents at beginning of period	14,949	15,096
Cash and cash equivalents at end of period	18,089	30,860
Supplemental cash flow information
Cash paid for interest	992	$ 902
Non-Cash Operating Activity
Increase to deferred revenue due to adoption of ASC Topic 606 - transition adjustment on January 1, 2018	$ 2,711