Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (4,784)	$ (6,391)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	40	135
Loss on impairment of fixed assets	48
Derivatives (gain) loss	12	(241)
Non-cash interest expense	1	1
Gain on sale of asset	(25)
Common stock issued to 401(k) plan	6	51
Share-based compensation expense	306	1,315
Non-cash investment (income) expense, net		(12)
Changes in operating assets and liabilities:
Prepaid expenses	(443)	(489)
Accounts payable	240	27
Accrued expenses and other liabilities	906	(536)
Net cash used in operating activities	(3,693)	(6,140)
Cash flows from investing activities:
Purchases of marketable securities		(6,761)
Sales of marketable securities		5,950
Disposals of property and equipment	25
Purchases of property and equipment		(16)
Net cash (used in) provided by investing activities	25	(827)
Cash flows from financing activities:
Proceeds from exercise of stock options		17
Proceeds from issuance of stock under ESPP	3	29
Repayment of loan payable	(110)	(103)
Repurchase of warrants	(14)
Proceeds from issuance of common stock, net of issuance costs	2,510
Net cash (used in) provided by financing activities	2,389	(57)
Increase (decrease) in cash, cash equivalents and restricted cash	(1,279)	(7,024)
Cash, cash equivalents and restricted cash at beginning of period	13,271	21,825	$ 21,825
Cash, cash equivalents and restricted cash at end of period	11,992	14,801	$ 13,271
Supplemental disclosure of cash flow information and non-cash investing and financing activities:
Cash paid for interest	14	$ 20
Issuance costs paid in common stock	$ 287