Schedule II - Condensed Financial Information of Registrant (Statements of Income (Parent Company)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Net investment (losses) gains									$ 154,488	$ 335,858	$ 267,005
Other income									681	805	376
Total revenues	$ 1,951,586	$ 1,937,902	$ 1,910,916	$ 1,891,247	$ 1,934,956	$ 2,031,342	$ 1,848,049	$ 1,870,418	7,691,651	7,684,764	7,654,184
Operating costs and expense									6,879,557	6,911,994	6,757,746
Income before income taxes									812,094	772,770	896,438
Federal income taxes:
Net expense (benefit)									(163,028)	(219,433)	(292,953)
Net income to common stockholders	$ 132,357	$ 161,920	$ 180,075	$ 166,397	$ 154,589	$ 162,054	$ 109,004	$ 123,447	640,749	549,094	601,916
Dividends from subsidiaries									639,477	694,462	700,664
Parent Company
Condensed Income Statements, Captions [Line Items]
Management fees and investment income including dividends from subsidiaries of $639,477, $694,462 and $700,664 for the years ended December 31, 2018, 2017 and 2016, respectively									697,687	738,923	726,742
Net investment (losses) gains									(1,685)	(4,286)	909
Other income									530	805	376
Total revenues									696,532	735,442	728,027
Operating costs and expense									191,873	182,145	171,967
Interest expense									155,082	146,929	139,216
Income before income taxes									349,577	406,368	416,844
Federal income taxes:
Federal income taxes provided by subsidiaries on a separate return basis									409,439	115,597	327,520
Federal income tax expense on a consolidated return basis									(113,138)	(195,261)	(246,389)
Net expense (benefit)									296,301	(79,664)	81,131
Income before undistributed equity in net income of subsidiaries									645,878	326,704	497,975
Equity in undistributed net (loss) income of subsidiaries									(5,129)	222,390	103,941
Net income to common stockholders									$ 640,749	$ 549,094	$ 601,916