CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 106,307	$ 144,353
Marketable securities	50,996	91,126
Restricted cash	28,234	30,314
Prepaid expenses and other current assets	17,774	22,037
Total current assets	203,311	287,830
Restricted cash	890	4,590
Property and equipment, net	35,987	40,184
Intangible assets, net	7,873	9,225
Goodwill	53,563	51,673
Other non-current assets	869	799
Total assets	302,493	394,301
Current liabilities:
Accounts payable	5,613	5,685
Accrued expenses	29,610	24,508
Accrued interest	5,078	5,078
Deferred revenue	25,625	30,079
Other current liabilities	7,749	1,056
Total current liabilities	73,675	66,406
Deferred revenue	2,500	2,500
Convertible notes payable	317,763	316,339
Other non-current liabilities	10,287	14,602
Total liabilities	404,225	399,847
Commitments and contingencies
Stockholders’ deficit:
Preferred stock, $0.01 par value, 2,000,000 shares authorized; no shares issued and outstanding at December 31, 2017 and 2016	0	0
Common stock, $0.01 par value, 600,000,000 shares authorized at December 31, 2017 and 2016; and 323,684,820 shares issued and 323,229,390 shares outstanding at December 31, 2017 and 271,701,397 shares issued and 271,245,967 shares outstanding at December 31, 2016	3,237	2,717
Additional paid-in capital	1,020,457	935,997
Accumulated deficit	(1,114,359)	(929,996)
Treasury stock, 455,430 shares, cost basis at both December 31, 2017 and 2016	(2,450)	(2,450)
Accumulated other comprehensive loss	(8,617)	(11,814)
Total stockholders’ deficit	(101,732)	(5,546)
Total liabilities and stockholders’ deficit	$ 302,493	$ 394,301