CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating activities:
Net income	$ 28,431	$ 62,055
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	99,464	68,035
Deferred income taxes	(10,705)	(38,442)
Stock–based compensation	16,115	20,654
Amortization of convertible senior notes and lease financing obligations	20,195	16,128
Other, net	3,875	14,406
Changes in operating assets and liabilities:
Receivables	(126,748)	(144,285)
Prepaid expenses and other assets	(51,582)	(27,552)
Medical claims and benefits payable	454,059	138,176
Accounts payable and accrued liabilities	314,391	20,991
Deferred revenue	68,640	(17,410)
Income taxes	25,063	(1,012)
Net cash provided by operating activities	841,198	111,744
Investing activities:
Purchases of investments	(616,324)	(627,953)
Proceeds from sales and maturities of investments	473,836	227,800
Purchases of equipment	(71,771)	(64,426)
Increase in restricted investments	(24,301)	(21,124)
Net cash paid in business combinations	(7,500)	(57,684)
Other, net	(15,220)	1,971
Net cash used in investing activities	(261,280)	(541,416)
Financing activities:
Proceeds from issuance of convertible senior notes, net of deferred financing costs	123,387	537,973
Proceeds from sale-leaseback transactions	0	158,694
Purchase of call option	0	(149,331)
Proceeds from issuance of warrants	0	75,074
Treasury stock purchases	0	(50,000)
Principal payments on term loan	0	(47,471)
Repayment of amounts borrowed under credit facility	0	(40,000)
Contingent consideration liabilities settled	(50,349)	0
Proceeds from employee stock plans	7,628	5,156
Other, net	2,117	363
Net cash provided by financing activities	82,783	490,458
Net increase in cash and cash equivalents	662,701	60,786
Cash and cash equivalents at beginning of period	935,895	795,770
Cash and cash equivalents at end of period	1,598,596	856,556
Supplemental cash flow information:
Income taxes	7,991	72,156
Interest	24,384	28,035
Schedule of non-cash investing and financing activities:
3.75% Notes exchanged for 1.625% Notes	176,551	0
Retirement of treasury stock	0	53,000
Increase in non-cash lease financing obligation – related party	13,841	19,222
Common stock used for stock-based compensation	8,595	6,667
Details of change in fair value of derivatives, net:
Change in fair value of derivatives, net	8	(3,383)
Business Combination, Description [Abstract]
Fair value of assets acquired	7,500	121,845
Fair value of contingent consideration liabilities incurred	0	(59,947)
Payable to seller	0	(3,882)
Escrow deposit	0	(332)
Net cash paid in business combinations	7,500	57,684
Gain on 1.125% Call Option
Details of change in fair value of derivatives, net:
Change in fair value of derivatives, net	36,646	42,332
Loss on 1.125% Notes Conversion Option
Details of change in fair value of derivatives, net:
Change in fair value of derivatives, net	(36,638)	(42,225)
Loss on 1.125% Warrants
Details of change in fair value of derivatives, net:
Change in fair value of derivatives, net	0	(3,923)
Gain on interest rate swap
Details of change in fair value of derivatives, net:
Change in fair value of derivatives, net	$ 0	$ 433