Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss	$ (7,748)	$ (18,829)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	248	236
Stock-based compensation expense	1,989	4,976
Changes in assets and liabilities
Prepaid expenses and other assets	(3,118)	(124)
Accounts payable	284	(695)
Deferred revenue	(146)
Accrued and other liabilities	(117)	(860)
Net cash used in operating activities	(8,608)	(15,296)
Cash flows from financing activities
Inducement on build-to-suit lease obligation		1,896
Proceeds from issuance of common stock in connection with employee benefit plans	13	35
Net cash provided by financing activities	13	1,931
Net change in cash, cash equivalents, and restricted cash	(8,595)	(13,365)
Cash, cash equivalents, and restricted cash at beginning of period	59,388	83,529
Cash, cash equivalents, and restricted cash at end of period	$ 50,793	$ 70,164