Consolidated Balance Sheets - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets, Current [Abstract]
Cash and cash equivalents	$ 64,065	$ 126,263
Short-term investments	22,678	26,012
Accounts receivable, net of allowances of $4	14	395
Prepaid expenses and other current assets	2,164	5,049
Total current assets	88,921	157,719
Property and equipment, net of accumulated depreciation and amortization of $61,741 and $60,006, respectively	1,176	295
Goodwill	44,543	44,543
Other assets	2,269	1,231
Total assets	136,909	203,788
Liabilities, Current [Abstract]
Accounts payable	9,152	5,469
Accrued liabilities	12,972	29,691
Current portion of long-term debt, net of deferred issuance costs	0	11,646
Total current liabilities	22,124	46,806
Other long-term liabilities	1,190	611
Total liabilities	23,314	47,417
Commitments and contingencies
Stockholders' Equity:
Preferred stock, $.01 par value; 5,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $.001 par value; 225,000 shares authorized; 106,679 and 106,162 shares issued, respectively	150	142
Additional paid-in capital	1,608,749	1,561,096
Accumulated deficit	(1,487,776)	(1,400,018)
Accumulated other comprehensive income (loss)	(10)	(6)
Treasury stock, at cost, 407 and 236 shares, respectively	(7,518)	(4,843)
Total stockholders' equity	113,595	156,371
Total liabilities and equity	$ 136,909	$ 203,788
Preferred stock, par value per share (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share (usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized	225,000	225,000