CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (59,780)	$ (50,878)	$ (151,184)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,929	4,858	3,577
Amortization of intangible assets	0	0	224
Amortization and premium of marketable securities, net	(729)	(1,140)	(1,048)
(Gain) loss on sale or disposal of assets	(55)	11	1,220
Goodwill impairment			90,976
Intangible asset impairment	18,000		18,677
Other asset impairment		1,800
Gain on fair value remeasurement of contingent consideration	(4,218)	(1,294)	(29,621)
Non-cash income tax benefit	(1,167)		(765)
Stock-based compensation expense	3,915	4,551	8,081
Changes in operating assets and liabilities:
Accounts and other receivables	(787)	2,274	(777)
Prepaid and other current assets	(334)	362	1,783
Other assets		(39)
Accounts payable and accrued expenses	1,638	(321)	(13,110)
Other liabilities	(816)	(6,599)	(3,268)
Net cash used in operating activities	(40,404)	(46,415)	(75,235)
Cash flows from investing activities:
Sales and maturities of marketable securities	123,600	113,173	201,469
Purchases of marketable securities	(220,321)	(95,382)	(171,182)
Acquisition of property and equipment	(1,552)	(731)	(813)
Proceeds from sale or disposal of assets	55	20	342
Net cash (used in) provided by investing activities	(98,218)	17,080	29,816
Cash flows from financing activities:
Net proceeds from stock issuances	170,792	16,248	29,022
Proceeds from issuance of stock from employee benefit plans	434	9	419
Issuance of term loan	2,962
Payment of term loan	(2,962)
Net cash provided by financing activities	171,226	16,257	29,441
Net increase (decrease) in cash and cash equivalents	32,604	(13,078)	(15,978)
Cash and cash equivalents at beginning of period	11,232	24,310	40,288
Cash and cash equivalents at end of period	43,836	11,232	24,310
Non-cash investing activities
Accrued construction in progress	$ 221	$ 25	107
Non-cash supplemental disclosure
Shares issued to former Kolltan executive for settlement of severance			$ 71