Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 133,174	$ 347,845
Marketable securities	201,710	125,710
Deferred tax assets	1,913	1,913
Prepaid expenses and other current assets	4,039	4,521
Total current assets	340,836	479,989
Marketable securities	134,430	18,448
Property and equipment, net	16,850	15,740
Intangible assets, net	27,278	28,219
Goodwill	13,128	13,128
Restricted cash and other non-current assets	1,294	1,215
Total assets	533,816	556,739
Current liabilities:
Accounts payable	2,551	2,954
Accrued expenses and other current liabilities	15,129	14,649
Deferred revenue, current portion	24,333	25,375
Total current liabilities	42,013	42,978
Deferred rent, net of current portion	8,456	8,674
Deferred revenue, net of current portion		5,302
Contingent consideration, net of current portion	6,670	6,321
Deferred tax liabilities	1,913	1,913
Other non-current liabilities	265	294
Total liabilities	59,317	65,482
Commitments and contingencies (Note 5)
Stockholders' equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2015 and December 31, 2014
Common stock, $0.01 par value, 125,000 shares authorized; 32,693 and 32,340 shares issued and outstanding at March 31, 2015 and December 31, 2014, respectively	327	323
Additional paid-in capital	646,466	638,389
Accumulated other comprehensive loss	(123)	(71)
Accumulated deficit	(172,171)	(147,384)
Total stockholders' equity	474,499	491,257
Total liabilities and stockholders' equity	$ 533,816	$ 556,739