Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income	$ 96,842	$ 162,845
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	37,106	27,744
Loss on disposal or abandonment of property, equipment and software	79	410
Deferred tax (benefit) expense	(8,349)	29
Compensation expense related to share-based payments	20,386	16,743
Non-cash interest expense	3,288	8,523
Amortization of investment premiums and other	9,964	11,165
Changes in assets and liabilities (decreasing) increasing cash flows from operations:
Premium receivables	(114,390)	(49,933)
Prepaid expenses, provider and other receivables and other current assets	3,133	(15,456)
Other long-term assets	(1,806)	(1,413)
Claims payable	196,969	33,851
Accounts payable, accrued expenses, contractual refunds payable and other current liabilities	(10,991)	41,721
Unearned revenue	144,821	8,308
Other long-term liabilities	(831)	(1,205)
Net cash provided by operating activities	376,221	243,332
Cash flows from investing activities:
Proceeds from sale or call of available-for-sale securities	891,492	734,486
Purchase of available-for-sale securities	(678,451)	(952,312)
Proceeds from redemption of investments on deposit for licensure	96,347	111,432
Purchase of investments on deposit for licensure	(156,033)	(121,941)
Purchase of property, equipment and software	(48,934)	(31,545)
Purchase of contract rights and related assets	(85,168)	0
Net cash provided by (used in) investing activities	19,253	(259,880)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	77,813	0
Issuance costs of long-term debt	(1,061)	0
Repayment of convertible notes principal	(259,880)	(120)
Payment of conversion premium on converted notes	0	(82)
Proceeds from convertible notes hedge instruments	0	82
Net increase (decrease) in bank overdrafts	5,557	(11,291)
Customer funds administered	(450)	3,164
Proceeds from exercise of stock options and employee stock purchases	15,509	43,133
Repurchase of common stock shares	0	(157,217)
Tax benefit related to share-based payments	6,311	13,414
Net cash used in financing activities	(156,201)	(108,917)
Net increase (decrease) in cash and cash equivalents	239,273	(125,465)
Cash and cash equivalents at beginning of period	546,811	763,946
Cash and cash equivalents at end of period	786,084	638,481
Supplemental disclosures of non-cash information:
Employee stock relinquished for payment of taxes	(4,337)	(3,621)
Unrealized gain on available-for-sale securities, net of tax	7,869	5,282
Common stock issued upon conversion of the 2.0% Convertible Senior Notes	129,431	0
Common stock received through hedge instruments upon conversion of the 2.0% Convertible Senior Notes	(129,431)	0
Reissuance of treasury stock for net share settlement of warrants	$ 153,778	$ 0