Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (26,195)	$ (26,497)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	746	1,602
Impairment of long-lived assets	0	5,784
Stock-based compensation expense	1,672	1,581
Write-off of lease receivable/prepaid commission assets	0	1,383
Changes in assets and liabilities
Prepaid expenses and other assets	(2,859)	962
Accounts payable	(512)	615
Deferred revenue	2,598	0
Accrued and other liabilities	716	(1,823)
Net cash used in operating activities	(23,834)	(16,393)
Cash flows from financing activities
Proceeds from issuance of common stock in connection with employee benefit plans	71	311
Proceeds from issuance of common stock in connection with exercise of options	285	0
Proceeds from issuance of common stock in private placement, net of issuance costs of $78	0	4,922
Net cash provided by financing activities	30,804	5,233
Net change in cash, cash equivalents, and restricted cash	6,970	(11,160)
Cash, cash equivalents, and restricted cash at beginning of period	62,971	67,557
Cash, cash equivalents, and restricted cash at end of period	69,941	56,397
Direct Offering [Member]
Cash flows from financing activities
Proceeds from issuance of common stock in offering	20,866	0
At-the-market Offering [Member]
Cash flows from financing activities
Proceeds from issuance of common stock in offering	$ 9,582	$ 0