CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 56,496	$ 106,307
Marketable securities	70,612	50,996
Restricted cash	17,586	28,234
Prepaid expenses and other current assets	15,847	17,774
Total current assets	160,541	203,311
Restricted cash	954	890
Property and equipment, net	29,343	35,987
Intangible assets, net	6,754	7,873
Goodwill	52,072	53,563
Other non-current assets	814	869
Total assets	250,478	302,493
Current liabilities:
Accounts payable	6,790	5,613
Accrued expenses	20,963	29,610
Accrued interest	2,031	5,078
Deferred revenue	15,365	25,625
Other current liabilities	1,566	7,749
Total current liabilities	46,715	73,675
Deferred revenue	2,500	2,500
Convertible notes payable	318,830	317,763
Other non-current liabilities	9,112	10,287
Total liabilities	377,157	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 September 30, 2018 and December 31, 2017, respectively	0	0
Common stock, $0.01 par value, 600,000,000 shares authorized at September 30, 2018 and December 31, 2017; 383,185,993 shares issued and 382,730,563 shares outstanding at September 30, 2018 and 323,684,820 shares issued and 323,229,390 shares outstanding at December 31, 2017	3,832	3,237
Additional paid-in capital	1,132,738	1,020,457
Accumulated deficit	(1,249,773)	(1,114,359)
Treasury stock, 455,430 shares, cost basis at both September 30, 2018 and December 31, 2017	(2,450)	(2,450)
Accumulated other comprehensive loss	(11,026)	(8,617)
Total stockholders' deficit	(126,679)	(101,732)
Total liabilities and stockholders' deficit	$ 250,478	$ 302,493