Segment Information (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
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
Net investment income																	55,494	45,166	69,613
Administrative services fees and other income																	6,294	(1,725)	34,791
Interest Expense																	33,309	31,376	32,614
Depreciation and amortization																	22,533	29,786	38,589
Share-based compensation expense																	29,451	28,334	29,930
Segment pretax income (loss)	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
Corporate/Other/Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues																	0	0	0
Net investment income																	0	0	0
Administrative services fees and other income																	0	0	0
Interest Expense																	0	0	0
Depreciation and amortization																	500	100	0
Share-based compensation expense																	0	0	0
Segment pretax income (loss)																	(118,200)	(185,300)	(12,000)
Net income (loss)																	(72,800)	(41,900)	(7,300)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues																	16,181,800	13,965,200	10,949,400
Operating Segments [Member] | Western Region Operations [Member]
Segment Reporting Information [Line Items]
Revenues																	15,553,300	13,361,200	10,377,100
Net investment income																	55,500	45,200	69,600
Administrative services fees and other income																	6,300	(1,700)	34,800
Interest Expense																	33,300	31,400	32,600
Depreciation and amortization																	22,000	29,700	38,600
Share-based compensation expense																	26,500	25,000	26,100
Segment pretax income (loss)																	547,400	315,600	207,500
Net income (loss)																	244,300	146,200	133,900
Operating Segments [Member] | Government Contracts [Member]
Segment Reporting Information [Line Items]
Revenues																	628,500	604,000	572,300
Net investment income																	0	0	0
Administrative services fees and other income																	0	0	0
Interest Expense																	0	0	0
Depreciation and amortization																	0	0	0
Share-based compensation expense																	3,000	3,300	3,800
Segment pretax income (loss)																	25,400	69,500	74,500
Net income (loss)																	14,200	41,300	43,500
Intersegment eliminations [Member]
Segment Reporting Information [Line Items]
Revenues																	0	0	0
Intersegment eliminations [Member] | Western Region Operations [Member]
Segment Reporting Information [Line Items]
Revenues																	13,800	12,400	11,100
Intersegment eliminations [Member] | Government Contracts [Member]
Segment Reporting Information [Line Items]
Revenues																	0	0	0
Intersegment eliminations [Member] | Corporate/Other/Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues																	$ (13,800)	$ (12,400)	$ (11,100)

[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.