CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 113,402	$ 106,307
Marketable securities	30,358	50,996
Restricted cash	19,548	28,234
Prepaid expenses and other current assets	17,726	17,774
Total current assets	181,034	203,311
Restricted cash	891	890
Property and equipment, net	32,422	35,987
Intangible assets, net	7,575	7,873
Goodwill	53,286	53,563
Other non-current assets	859	869
Total assets	276,067	302,493
Current liabilities:
Accounts payable	5,770	5,613
Accrued expenses	19,225	29,610
Accrued interest	2,031	5,078
Deferred revenue	16,377	25,625
Other current liabilities	1,501	7,749
Total current liabilities	44,904	73,675
Deferred revenue	2,500	2,500
Convertible notes payable	318,119	317,763
Other non-current liabilities	9,913	10,287
Total liabilities	375,436	404,225
Commitments and contingencies	0	0
Stockholders’ deficit:
Preferred stock, $0.01 par value, 2,000,000 shares authorized; no shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	0	0
Common stock, $0.01 par value, 600,000,000 shares authorized at March 31, 2018 and December 31, 2017; 347,204,416 shares issued and 346,748,986 shares outstanding at March 31, 2018 and 323,684,820 shares issued and 323,229,390 shares outstanding at December 31, 2017	3,472	3,237
Additional paid-in capital	1,069,391	1,020,457
Accumulated deficit	(1,160,711)	(1,114,359)
Treasury stock, 455,430 shares, cost basis at both March 31, 2018 and December 31, 2017	(2,450)	(2,450)
Accumulated other comprehensive loss	(9,071)	(8,617)
Total stockholders’ deficit	(99,369)	(101,732)
Total liabilities and stockholders’ deficit	$ 276,067	$ 302,493