Quarterly Results of Operations (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 2,828,591	$ 2,438,634	$ 2,630,340	$ 2,520,613	$ 2,697,413	$ 2,716,588	$ 2,833,020	$ 2,657,173	$ 10,418,178	$ 10,904,194	$ 10,318,353
Total benefits and expenses	2,621,848	2,298,497	2,416,550	2,336,488	2,420,670	2,484,773	2,532,485	2,457,733	9,673,383	9,895,661	9,683,099
Income before income taxes	206,743	140,137	213,790	184,125	276,743	231,815	300,535	199,440	744,795	1,008,533	635,254
Net Income (Loss) Attributable to Parent	$ 163,127	$ 83,534	$ 130,391	$ 125,114	$ 191,091	$ 157,996	$ 198,296	$ 136,664	$ 502,166	$ 684,047	$ 418,837
Basic earnings per share:
Earnings Per Share, Basic (in dollars per share)	$ 2.49	$ 1.26	$ 1.97	$ 1.84	$ 2.78	$ 2.30	$ 2.87	$ 1.94	$ 7.55	$ 9.88	$ 5.82
Earnings Per Share, Diluted (in dollars per share)	$ 2.46	$ 1.25	$ 1.94	$ 1.81	$ 2.75	$ 2.28	$ 2.84	$ 1.92	$ 7.46	$ 9.78	$ 5.78