Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 216,001	$ 278,887
Marketable securities	418,067	425,491
Tenant improvements receivable	21,228	8,542
Prepaid expenses	8,730	8,209
Other current assets	3,285	3,085
Total current assets	667,311	724,214
Marketable securities	165,801	180,452
Property and equipment, net	181,720	156,955
Intangible assets, net	19,753	20,694
Goodwill	13,128	13,128
Restricted cash and other non-current assets	24,857	22,679
Total assets	1,072,570	1,118,122
Current liabilities:
Accounts payable	8,769	13,664
Accrued expenses and other current liabilities	44,307	54,660
Deferred revenue, current portion	19,560	6,209
Total current liabilities	72,636	74,533
Deferred rent, net of current portion	10,882	10,408
Deferred revenue, net of current portion	22,883	40,204
Contingent consideration, net of current portion	3,130	3,277
Financing lease obligation, net of current portion	147,555	120,140
Other non-current liabilities	105	120
Total liabilities	257,191	248,682
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2017 and December 31, 2016
Common stock, $0.01 par value, 125,000 shares authorized; 40,923 and 40,691 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	409	407
Additional paid-in capital	1,463,098	1,447,856
Accumulated other comprehensive loss	(1,252)	(1,149)
Accumulated deficit	(646,876)	(577,674)
Total stockholders’ equity	815,379	869,440
Total liabilities and stockholders’ equity	$ 1,072,570	$ 1,118,122