CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOW - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (16,538)	$ (12,625)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	775	1,165
Amortization and premium of marketable securities, net	(48)	(63)
Gain on sale or disposal of assets	(24)
Loss on fair value remeasurement of contingent consideration	483	234
Stock-based compensation expense	1,275	687
Changes in operating assets and liabilities:
Accounts and other receivables	(26)	(93)
Prepaid and other current assets	(2,137)	206
Accounts payable and accrued expenses	(1,266)	(853)
Other liabilities	(578)	(768)
Net cash used in operating activities	(18,084)	(12,110)
Cash flows from investing activities:
Sales and maturities of marketable securities	78,000	22,200
Purchases of marketable securities	(33,970)
Acquisition of property and equipment	(567)	(235)
Proceeds from sale or disposal of assets	24
Net cash provided by investing activities	43,487	21,965
Cash flows from financing activities:
Net proceeds from stock issuances		1,613
Proceeds from issuance of stock from employee benefit plans	74	24
Net cash provided by financing activities	74	1,637
Net increase in cash and cash equivalents	25,477	11,492
Cash and cash equivalents at beginning of period	43,836	11,232
Cash and cash equivalents at end of period	$ 69,313	22,724
Non-cash investing activities
Accrued construction in progress		$ 462