Parent Financial Statements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Current assets:
Cash and cash equivalents	$ 546,811	$ 763,946	$ 505,915	$ 763,272
Short-term investments	394,346	230,007
Deferred income taxes	24,720	28,063
Prepaid expenses	37,851	13,538
Other current assets	20,755	7,083
Total current assets	1,165,760	1,158,701
Long-term investments	1,118,127	639,165
Property, equipment and software, net of accumulated depreciation of $172,132 and $145,375 at December 31, 2011 and 2010, respectively	110,602	96,967
Other long-term assets	18,300	13,220
Total assets	2,801,348	2,283,388
Current liabilities:
Accrued payroll and related liabilities	63,475	71,253
Accounts payable, accrued expenses and other	149,353	121,283
Current portion of long-term debt	256,995	0
Total current liabilities	1,084,174	850,841
Long-term debt	400,000	245,750
Deferred income taxes	19,447	7,393
Other long-term liabilities	13,208	13,767
Total liabilities	1,516,829	1,117,751
Stockholders' equity:
Common stock, $0.01 par value. Authorized 100,000,000 shares; outstanding 46,878,474 and 48,167,229 at December 31, 2011 and 2010, respectively	573	554
Additional paid-in capital	637,605	543,611
Accumulated other comprehensive income	11,942	627
Retained earnings	1,059,624	864,003
Stockholders' equity before treasury stock	1,709,744	1,408,795
Less treasury stock at cost (11,201,634 and 7,759,234 shares at December 31, 2011 and 2010, respectively)	(425,225)	(243,158)
Total stockholders' equity	1,284,519	1,165,637	984,444	872,659
Total liabilities and stockholders' equity	2,801,348	2,283,388
Parent Company [Member]
Current assets:
Cash and cash equivalents	101,084	62,189	58,326	256,126
Short-term investments	282,888	54,895
Due from subsidiaries	13,608	34,397
Deferred income taxes	9,321	8,445
Prepaid expenses	30,864	10,366
Other current assets	3,532	3,245
Total current assets	441,297	173,537
Long-term investments	340,857	131,523
Investment in subsidiaries	1,168,595	1,128,535
Property, equipment and software, net of accumulated depreciation of $172,132 and $145,375 at December 31, 2011 and 2010, respectively	97,648	84,428
Deferred income taxes	20,043	20,074
Other long-term assets	16,317	10,734
Total assets	2,084,757	1,548,831
Current liabilities:
Accrued payroll and related liabilities	63,475	71,254
Accounts payable, accrued expenses and other	55,292	47,192
Current portion of long-term debt	256,995	0
Total current liabilities	375,762	118,446
Long-term debt	400,000	245,750
Deferred income taxes	11,268	5,231
Other long-term liabilities	13,208	13,767
Total liabilities	800,238	383,194
Stockholders' equity:
Common stock, $0.01 par value. Authorized 100,000,000 shares; outstanding 46,878,474 and 48,167,229 at December 31, 2011 and 2010, respectively	573	554
Additional paid-in capital	637,605	543,611
Accumulated other comprehensive income	11,942	627
Retained earnings	1,059,624	864,003
Stockholders' equity before treasury stock	1,709,744	1,408,795
Less treasury stock at cost (11,201,634 and 7,759,234 shares at December 31, 2011 and 2010, respectively)	(425,225)	(243,158)
Total stockholders' equity	1,284,519	1,165,637
Total liabilities and stockholders' equity	$ 2,084,757	$ 1,548,831