CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Net premiums	$ 9,841,130	$ 9,248,871	$ 8,570,741
Investment income, net of related expenses	2,154,651	1,911,886	1,734,495
Investment related gains (losses), net:
Other-than-temporary impairments on fixed maturity securities	(42,639)	(38,805)	(57,380)
Other-than-temporary impairments on fixed maturity securities transferred to other comprehensive income	0	74	0
Other investment related gains (losses), net	210,519	132,926	(107,370)
Total investment related gains (losses), net	167,880	94,195	(164,750)
Other revenues	352,108	266,559	277,692
Total revenues	12,515,769	11,521,511	10,418,178
Benefits and expenses
Claims and other policy benefits	8,518,917	7,993,375	7,489,382
Interest credited	502,040	364,691	336,964
Policy acquisition costs and other insurance expenses	1,466,646	1,310,540	1,127,486
Other operating expenses	710,690	645,509	554,044
Interest expense	146,025	137,623	142,863
Collateral finance and securitization expense	28,636	25,827	22,644
Total benefits and expenses	11,372,954	10,477,565	9,673,383
Income before income taxes	1,142,815	1,043,946	744,795
Provision for income taxes	(679,366)	342,503	242,629
Net income	$ 1,822,181	$ 701,443	$ 502,166
Earnings per share
Basic earnings per share (in dollars per share)	$ 28.28	$ 10.91	$ 7.55
Diluted earnings per share (in dollars per share)	27.71	10.79	7.46
Dividends declared per share	$ 1.82	$ 1.56	$ 1.40