Parent Financial Statements (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 32,776	$ 48,074	$ 44,294	$ 70,477	$ 79,628	$ 84,348	$ 67,213	$ 42,182	$ 195,621	$ 273,371	$ 149,279
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization									37,369	35,048	34,746
Loss on disposal or abandonment of property, equipment and software									646	354	585
Deferred tax expense (benefit)									9,055	(2,262)	818
Compensation expense related to share-based payments									22,868	19,635	15,936
Non-cash interest expense									11,454	10,646	9,974
Gain on sale of contract rights											(5,810)
Amortization (accretion) of investment premiums (discounts) and other									15,039	9,219	(167)
Changes in assets and liabilities (decreasing) increasing cash flows from operations:
Other assets									(1,820)	(691)	(1,146)
Accounts payable, accrued expenses and other current liabilities									9,624	61,967	(43,758)
Other long-term liabilities									(559)	1,408	(1,480)
Net cash provided by operating activities									207,989	401,949	147,034
Cash flows from investing activities:
Purchase of property, equipment and software									(49,847)	(29,463)	(29,738)
Proceeds from sale of contract rights											5,810
Net cash used in investing activities									(707,193)	(80,652)	(296,645)
Cash flows from financing activities:
Proceeds from issuance of long-term debt									400,000
Issuance costs of long-term debt									(5,793)
Repayment of convertible notes principal									(120)
Payment of conversion premium on converted notes									(82)
Proceeds from convertible notes hedge instruments									82
Repayment of borrowings under credit facility											(44,318)
Proceeds from exercise of stock options and employee stock purchases									52,554	26,466	10,698
Repurchase of common stock shares									(175,718)	(138,540)	(69,751)
Tax benefit related to share-based payments									18,677	3,097	842
Net cash provided by (used in) financing activities									282,069	(63,266)	(107,746)
Net (decrease) increase in cash and cash equivalents									(217,135)	258,031	(257,357)
Cash and cash equivalents at beginning of year				763,946				505,915	763,946	505,915	763,272
Cash and cash equivalents at end of year	546,811				763,946				546,811	763,946	505,915
Parent Company [Member]
Cash flows from operating activities:
Net income									195,621	273,371	149,279
Adjustments to reconcile net income to net cash provided by operating activities:
Equity earnings in subsidiaries									(188,516)	(242,484)	(85,054)
Depreciation and amortization									32,442	28,375	27,256
Loss on disposal or abandonment of property, equipment and software									399	361	121
Deferred tax expense (benefit)									(1,150)	(9,937)	(9,467)
Compensation expense related to share-based payments									22,868	19,635	15,936
Non-cash interest expense									11,454	10,646	9,974
Gain on sale of contract rights											(5,810)
Amortization (accretion) of investment premiums (discounts) and other									6,945	(152)	(2,763)
Changes in assets and liabilities (decreasing) increasing cash flows from operations:
Prepaid expenses and other current assets									(20,230)	(683)	(2,397)
Other assets									(1,835)	(689)	(1,146)
Accounts payable, accrued expenses and other current liabilities									(6,028)	32,990	(28,215)
Other long-term liabilities									(559)	1,408	(1,480)
Net cash provided by operating activities									51,411	112,841	66,234
Cash flows from investing activities:
Purchase of securities, net									(438,751)	(14,541)	(115,115)
Purchase of property, equipment and software									(44,746)	(27,814)	(24,656)
Contributions made to subsidiaries									(14,752)	(11,012)	(70,104)
Dividends received from subsidiaries									175,344	61,687	71,700
Proceeds from sale of contract rights											5,810
Net cash used in investing activities									(322,905)	8,320	(132,365)
Cash flows from financing activities:
Proceeds from issuance of long-term debt									400,000
Issuance costs of long-term debt									(5,793)
Repayment of convertible notes principal									(120)
Payment of conversion premium on converted notes									(82)
Proceeds from convertible notes hedge instruments									82
Change in due from and due to subsidiaries, net									20,789	(8,321)	(29,140)
Repayment of borrowings under credit facility											(44,318)
Proceeds from exercise of stock options and employee stock purchases									52,554	26,466	10,698
Repurchase of common stock shares									(175,718)	(138,540)	(69,751)
Tax benefit related to share-based payments									18,677	3,097	842
Net cash provided by (used in) financing activities									310,389	(117,298)	(131,669)
Net (decrease) increase in cash and cash equivalents									38,895	3,863	(197,800)
Cash and cash equivalents at beginning of year				62,189				58,326	62,189	58,326	256,126
Cash and cash equivalents at end of year	$ 101,084				$ 62,189				$ 101,084	$ 62,189	$ 58,326