Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues	$ 4,036,400		$ 4,153,700		$ 4,163,600		$ 3,889,900		$ 3,758,400		$ 3,789,900		$ 3,421,400		$ 3,038,900		$ 16,243,587	$ 14,008,586	$ 11,053,743
Health plan services expenses	3,216,000		3,318,400		3,363,700		3,142,900		3,038,200		3,104,000		2,763,200		2,402,300		13,041,036	11,307,751	8,886,547
Government contracts costs	165,900		158,100		137,300		142,500		147,100		124,400		133,200		132,000		603,841	536,643	502,918
Income (loss) from operations before income taxes	101,500	[1],[2]	153,300	[3],[4]	132,100	[5],[6]	67,700	[7],[8]	16,300	[9],[10]	22,700	[11],[12]	98,800	[13]	62,000	[14]	454,644	199,792	269,953
Net income (loss)	$ 37,100	[1],[2]	$ 60,300	[3],[4]	$ 58,400	[5],[6]	$ 30,000	[7],[8]	$ 4,900	[9],[10]	$ (8,900)	[11],[12]	$ 120,900	[13],[15]	$ 28,800	[14]	$ 185,677	$ 145,629	$ 170,126
Basic (loss) earnings per share (usd per share)	$ 0.48		$ 0.78		$ 0.76		$ 0.39		$ 0.06		$ (0.11)		$ 1.51		$ 0.36		$ 2.40	$ 1.83	$ 2.14
Diluted (loss) earnings per share (usd per share)	$ 0.47	[16]	$ 0.77	[16]	$ 0.75	[16]	$ 0.38	[16]	$ 0.06	[17]	$ (0.11)	[17]	$ 1.49	[17]	$ 0.36	[17]	$ 2.37	$ 1.80	$ 2.12
Other ACA fees	$ 21,100		$ 22,200		$ 21,500		$ 20,800		$ 25,800		$ 26,600		$ 22,500		$ 22,500
Tax Benefit Due to Worthless Stock loss													72,600					$ 73,700
Asset impairment							1,900		3,800		84,700						$ 1,884	88,536	$ 0
Expenses primarily related to master services agreement	22,700		21,700		26,400		44,300		68,300		21,100
Health plan services premiums																	15,553,348	13,361,170	10,377,073
ACA Health Insurer Fee [Member]
Amortization of deferred cost	$ 58,200		$ 58,400		$ 58,500		$ 57,800		$ 35,400		$ 31,900		$ 37,800		$ 36,300		233,000	141,400
Medicaid Premium Revenue [Member]
Health plan services premiums																	$ 6,429,600	$ 4,755,900	$ 2,430,300

[1] Includes $22.7 million in pretax expenses primarily related to the Cognizant Transaction.

[2] Includes $58.2 million amortization of deferred costs of health insurer's fee and $21.1 million in other ACA fees.

[3] Includes $21.7 million in pretax expenses primarily related to the Cognizant Transaction.

[4] Includes $58.4 million amortization of deferred costs of health insurer's fee and $22.2 million in other ACA fees.

[5] Includes $26.4 million in pretax expenses primarily related to the Cognizant Transaction.

[6] Includes $58.5 million amortization of deferred costs of health insurer's fee and $21.5 million in other ACA fees.

[7] Includes $1.9 million pretax asset impairment and $44.3 million in pretax expenses primarily related to the Cognizant Transaction.

[8] Includes $57.8 million amortization of deferred costs of health insurer's fee and $20.8 million in other ACA fees.

[9] Includes $3.8 million pretax asset impairment primarily related to our assets held for sale in connection with the Cognizant Transaction and $68.3 million in pretax expenses primarily related to the Cognizant Transaction.

[10] Includes $35.4 million amortization of deferred costs of health insurer's fee and $25.8 million in other ACA fees.

[11] Includes $31.9 million amortization of deferred costs of health insurer's fee and $26.6 million in other ACA fees.

[12] Includes $84.7 million pretax asset impairment related to our assets held for sale in connection with the Cognizant Transaction and $21.1 million in pretax expenses primarily related to the Cognizant transaction.

[13] Includes $37.8 million amortization of deferred costs of health insurer's fee and $22.5 million in other ACA fees.

[14] Includes $36.3 million amortization of deferred costs of health insurer's fee and $22.5 million in other ACA fees.

[15] Includes tax benefit of $72.6 million, net of adjustments, as a result of a loss on the stock of one of our subsidiaries.

[16] The sum of the quarterly amounts may not equal the year-to-date amounts due to rounding.

[17] The sum of the quarterly amounts may not equal the year-to-date amounts due to rounding.