Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
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:
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 intangible assets		(4,000)
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:
Premium receivables	(23,307)	21,664	(18,272)
Prepaid expenses, provider and other receivables and other current assets	(28,487)	(10,818)	(2,310)
Other assets	(1,820)	(691)	(1,146)
Claims payable	62,773	(18,361)	(7,071)
Accounts payable, accrued expenses, contractual refunds payable and other current liabilities	9,624	61,967	(43,758)
Unearned revenue	(102,287)	4,769	15,710
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:
Proceeds from sale of trading securities		12,000	5,850
Proceeds from sale or call of available-for-sale securities	1,069,141	1,063,119	299,239
Purchase of available-for-sale securities	(1,713,571)	(1,104,496)	(648,670)
Proceeds from redemption of held-to-maturity securities			273,125
Purchase of held-to-maturity securities			(194,851)
Proceeds from redemption of investments on deposit for licensure	132,963	86,345	72,164
Purchase of investments on deposit for licensure	(145,879)	(98,737)	(79,574)
Purchase of property, equipment and software	(49,847)	(29,463)	(29,738)
Proceeds from sale of intangible assets		4,000
Proceeds from sale of contract rights			5,810
Purchase of contract rights and related assets		(13,420)
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)
Net (decrease) increase in bank overdrafts	(10,691)	40,890	(2,492)
Customer funds administered	3,160	4,821	(2,725)
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	763,272
Cash and cash equivalents at end of year	546,811	763,946	505,915
Supplemental disclosures of cash flow information:
Cash paid for interest	5,348	5,380	6,302
Cash paid for income taxes	110,255	169,890	51,745
Supplemental disclosures of non-cash information:
Auction rate securities pending settlement	3,439
Employee stock relinquished for payment of taxes	(6,349)	(1,795)	(591)
Employee stock relinquished for stock option exercises			(344)
Transfer of held-to-maturity securities to available-for-sale securities			424,237
Transfer of held-to-maturity investments on deposit to available-for-sale investment on deposit			98,458
Unrealized gain on held-to-maturity investment portfolio at time of transfer to available-for-sale, net of tax			3,030
Unrealized gain (loss) on available-for-sale securities, net of tax	$ 11,315	$ (727)	$ 2,346