Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities
Net loss	$ (15,109)	$ (15,837)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	493	1,153
Impairment of long-lived assets	0	2,870
Stock-based compensation expense	1,045	1,205
Write-off lease receivable/prepaid commission assets	0	1,383
Changes in assets and liabilities
Prepaid expenses and other assets	(3,117)	637
Accounts payable	1,101	(177)
Deferred revenue	2,010	0
Accrued and other liabilities	(1,594)	(1,330)
Net cash used in operating activities	(15,171)	(10,096)
Cash flows from financing activities
Proceeds from issuance of common stock in connection with employee benefit plans	71	108
Proceeds from issuance of common stock in connection with exercise of options	280	0
Proceeds from issuance of common stock in private placement, net of issuance costs	0	4,922
Net cash provided by financing activities	30,067	5,030
Net change in cash, cash equivalents, and restricted cash	14,896	(5,066)
Cash, cash equivalents, and restricted cash at beginning of period	62,971	67,557
Cash, cash equivalents, and restricted cash at end of period	77,867	62,491
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	$ 8,850	$ 0