CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating activities:
Net income (loss)	$ 54,486,000	$ (19,217,000)
Adjustments to reconcile net income (loss) to net cash (used in) provided by operating activities:
Depreciation and amortization	43,907,000	38,010,000
Deferred income taxes	(22,155,000)	(1,264,000)
Stock-based compensation	12,150,000	9,812,000
Gain on sale of subsidiary	0	(1,747,000)
Amortization of convertible senior notes	9,688,000	2,915,000
Change in fair value of derivatives	3,384,000	1,086,000
Amortization of premium/discount on investments	4,298,000	3,615,000
Amortization of deferred financing costs	2,366,000	515,000
Tax deficiency from employee stock compensation	(38,000)	(50,000)
Changes in operating assets and liabilities:
Receivables	(64,094,000)	6,891,000
Prepaid expenses and other current assets	(22,856,000)	(10,352,000)
Medical claims and benefits payable	(29,043,000)	123,062,000
Accounts payable and accrued liabilities	(16,968,000)	(22,982,000)
Deferred revenue	(95,849,000)	125,426,000
Income taxes	8,976,000	(19,737,000)
Net cash (used in) provided by operating activities	(111,748,000)	235,983,000
Investing activities:
Purchases of equipment	(35,229,000)	(33,301,000)
Purchases of investments	(532,151,000)	(144,348,000)
Sales and maturities of investments	149,420,000	136,772,000
Proceeds from sale of subsidiary, net of cash surrendered	0	9,162,000
Change in deferred contract costs	6,994,000	(23,055,000)
Increase in restricted investments	(12,834,000)	(2,154,000)
Change in other non-current assets and liabilities	(8,012,000)	(4,383,000)
Net cash used in investing activities	(431,812,000)	(61,307,000)
Financing activities:
Proceeds from issuance of 1.125% Notes, net of deferred issuance costs	537,973,000	0
Proceeds from sale-leaseback transactions	158,694,000	0
Purchase of 1.125% Notes call option	(149,331,000)	0
Proceeds from issuance of warrants	75,074,000	0
Treasury stock purchases	(50,000,000)	0
Repayment of amounts borrowed under credit facility	(40,000,000)	(10,000,000)
Amount borrowed under credit facility	0	60,000,000
Principal payments on term loan	(47,471,000)	(573,000)
Settlement of interest rate swap	(875,000)	0
Proceeds from employee stock plans	4,852,000	5,485,000
Excess tax benefits from employee stock compensation	1,544,000	3,677,000
Net cash provided by financing activities	490,460,000	58,589,000
Net (decrease) increase in cash and cash equivalents	(53,100,000)	233,265,000
Cash and cash equivalents at beginning of period	795,770,000	493,827,000
Cash and cash equivalents at end of period	742,670,000	727,092,000
Supplemental cash flow information:
Income taxes	41,407,000	1,074,000
Interest	21,933,000	4,719,000
Schedule of non-cash investing and financing activities:
Retirement of treasury stock	53,000,000	0
Common stock used for stock-based compensation	5,669,000	9,390,000
Details of change in fair value of derivatives:
Change in fair value of derivatives	(3,384,000)	(1,086,000)
Details of sale of subsidiary:
Decrease in carrying value of assets	0	30,942,000
Decrease in carrying value of liabilities	0	(23,527,000)
Gain on sale	0	1,747,000
Proceeds from sale of subsidiary, net of cash surrendered	0	9,162,000
Gain on 1.125% Call Option
Details of change in fair value of derivatives:
Change in fair value of derivatives	57,792,000	0
Loss on embedded cash conversion option
Details of change in fair value of derivatives:
Change in fair value of derivatives	(57,686,000)	0
Loss on 1.125% Warrants
Details of change in fair value of derivatives:
Change in fair value of derivatives	(3,923,000)	0
Gain (loss) on interest rate swap
Details of change in fair value of derivatives:
Change in fair value of derivatives	$ 433,000	$ (1,086,000)