Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 192,499	$ 206,279
Deferred tax assets	693	693
Prepaid expenses and other current assets	2,728	5,015
Total current assets	195,920	211,987
Property and equipment, net	11,984	10,920
Restricted cash and other non-current assets	1,606	1,483
Total assets	209,510	224,390
Current liabilities:
Accounts payable	2,601	4,359
Accrued expenses and other current liabilities	5,190	5,175
Deferred revenue, current portion	25,255	25,340
Total current liabilities	33,046	34,874
Deferred rent, net of current portion	7,263	6,740
Deferred revenue, net of current portion	23,958	30,208
Deferred tax liabilities	693	693
Other non-current liabilities	385	208
Total liabilities	65,345	72,723
Commitments and contingencies (Note 4)
Stockholders' equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2014 and December 31, 2013
Common stock, $0.01 par value, 125,000 shares authorized; 24,279 and 23,940 shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively	243	239
Additional paid-in capital	253,206	250,103
Accumulated deficit	(109,284)	(98,675)
Total stockholders' equity	144,165	151,667
Total liabilities and stockholders' equity	$ 209,510	$ 224,390