Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net loss	$ (17,723)	$ (12,731)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	58	264
Loss on impairment of fixed assets	48
Derivatives (gain) loss	10,198	(795)
Non-cash interest expense	2	2
Common stock issued to 401(k) plan	6	113
Gain on lease assignment	(603)
Share-based compensation expense	456	2,583
Non-cash investment (income) expense, net		8
Changes in operating assets and liabilities:
Prepaid expenses	(700)	(206)
Other assets	(6)	5
Accounts payable	(74)	(133)
Accrued expenses and other liabilities	1,566	(89)
Net cash used in operating activities	(6,772)	(10,979)
Cash flows from investing activities:
Purchases of marketable securities		(8,256)
Sales of marketable securities		12,300
Purchases of property and equipment	(65)	(54)
Net cash (used in) provided by investing activities	(65)	3,990
Cash flows from financing activities:
Proceeds from exercise of stock options		26
Proceeds from issuance of stock under ESPP	3	29
Proceeds from exercise of warrants	10
Repayment of loan payable	(522)	(208)
Repurchase of warrants	(14)
Proceeds from issuance of common stock and warrants, net of commissions and issuance costs	16,511
Net cash (used in) provided by financing activities	15,988	(153)
Increase (decrease) in cash and cash equivalents and restricted cash	9,151	(7,142)
Cash, cash equivalents and restricted cash at beginning of period	13,271	21,825
Cash, cash equivalents and restricted cash at end of period	22,422	14,683
Supplemental disclosure of cash flow information and non-cash investing and financing activities:
Cash paid for interest	25	$ 40
Issuance costs paid in common stock	$ 287