Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (18,218)	$ (76,333)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	498	1,060
Write-off of acquired in-process research & development		38,313
Stock-based compensation expense	3,399	16,139
Changes in assets and liabilities, net of acquisition
Prepaid expenses and other assets	(2,782)	(224)
Accounts payable	652	(1,744)
Deferred revenue	(146)	(1,371)
Accrued and other liabilities	(484)	(5,097)
Net cash used in operating activities	(17,081)	(29,257)
Cash flows from investing activities
Purchase of property and equipment		(33)
Cash paid to acquire in-process research & development		(2,076)
Cash acquired in the merger transaction		5,277
Net cash provided by investing activities		3,168
Cash flows from financing activities
Inducement on build-to-suit lease obligation		1,896
Proceeds from issuance of common stock, net of issuance costs	25,127
Proceeds from issuance of common stock in connection with employee benefit plans and exercise of stock options	123	52
Net cash provided by financing activities	25,250	1,948
Net increase (decrease) in cash, cash equivalents and restricted cash	8,169	(24,141)
Cash, cash equivalents and restricted cash at beginning of period	59,388	83,529
Cash, cash equivalents and restricted cash at end of period	67,557	59,388
Supplemental disclosure of noncash items
Issuance of common stock for the merger transaction		$ 37,331
Property and equipment recorded upon adoption of ASU 2016-02	$ 2,151