CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (19,717)	$ (20,487)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	45	57
Loss on retirement of property and equipment		5
Accretion and amortization on investments, net	(521)	213
Change in fair value of equity investment, including foreign currency translation	338
Stock-based compensation for services by non-employees	155	159
Stock-based compensation for employees and directors	4,774	6,152
Amortization related to 401(k) contributions	10	32
Changes in assets and liabilities:
Current assets	(1,034)	(401)
Current liabilities	(2,049)	(1,899)
Net cash used in operating activities	(17,999)	(16,169)
Cash flows from investing activities:
Purchases of property and equipment	(9)
Purchases of marketable securities	(149,720)	(81,260)
Proceeds from maturities of marketable securities	71,163	94,486
Net cash (used in) provided by investing activities	(78,566)	13,226
Cash flows from financing activities:
Proceeds from issuances of common stock, net of issuance costs	92,960	37
Net cash provided by financing activities	92,960	37
Net decrease in cash, cash equivalents and restricted cash	(3,605)	(2,906)
Cash, cash equivalents and restricted cash at the beginning of the period	16,603	13,078
Cash, cash equivalents and restricted cash at the end of the period	$ 12,998	$ 10,172