Schedule II - Condensed Financial Information of Registrant (Statements of Income (Parent Company)) (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
Condensed Income Statements, Captions [Line Items]
Other income									$ 337	$ 1,308	$ 1,026
Total revenues	$ 1,811,056	$ 1,860,957	$ 1,789,765	$ 1,744,679	$ 1,784,428	$ 1,840,605	$ 1,796,989	$ 1,706,906	7,206,457	7,128,928	6,408,534
Operating costs and expense									6,474,427	6,176,732	5,709,646
Income before income taxes									732,030	952,196	698,888
Federal income taxes:
Net expense									(227,923)	(302,593)	(193,587)
Net income to common stockholders	$ 109,745	$ 152,607	$ 123,035	$ 118,307	$ 110,711	$ 188,539	$ 179,961	$ 169,673	503,694	648,884	499,925
Dividends from subsidiaries									642,421	503,483	269,626
Parent Company
Condensed Income Statements, Captions [Line Items]
Management fees and investment income including dividends from subsidiaries of $642,421, $503,483, and $269,626 for the years ended December 31, 2015, 2014 and 2013, respectively									655,318	515,775	277,223
Net investment gains									696	5,487	24,550
Other income									348	450	223
Total revenues									656,362	521,712	301,996
Operating costs and expense									143,391	148,288	122,562
Interest expense									128,248	125,352	120,066
Income before income taxes									384,723	248,072	59,368
Federal income taxes:
Federal income taxes provided by subsidiaries on a separate return basis									272,180	366,721	225,845
Federal income tax expense on a consolidated return basis									(199,322)	(273,310)	(154,928)
Net expense									72,858	93,411	70,917
Income before undistributed equity in net income of subsidiaries									457,581	341,483	130,285
Equity in undistributed net income of subsidiaries									46,113	307,401	369,640
Net income to common stockholders									$ 503,694	$ 648,884	$ 499,925