Statutory Information and Restrictions (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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statutory Information and Restrictions [Line Items]
Statutory capital and surplus of insurance subsidiaries	$ 883,870				$ 861,421								$ 883,870	$ 861,421
Deferred policy acquisition costs	253,176				215,082								253,176	215,082
Difference in policyholder reserves	95,536				87,345								95,536	87,345
Goodwill	47,396				47,396								47,396	47,396
Investment fair value adjustments on fixed maturities	314,705				519,593								314,705	519,593
Difference in investment reserves	120,795				118,633								120,795	118,633
Federal income tax liability	(224,492)				(290,034)								(224,492)	(290,034)
Net funded status of pension and other postretirement benefit obligations	(18,213)				(20,027)								(18,213)	(20,027)
Non-admitted assets and other, net	21,691				18,528								21,691	18,528
Shareholders' equity of parent company and non-insurance subsidiaries	19,543				16,465								19,543	16,465
Parent company short-term and long-term debt	(249,346)				(237,939)								(249,346)	(237,939)
Total shareholders' equity	1,264,661				1,336,463				$ 1,099,305				1,264,661	1,336,463	$ 1,099,305
Statutory net income of insurance subsidiaries													87,619	97,875	98,905
Net loss of non-insurance companies													(4,474)	(3,906)	(4,583)
Interest expense													(13,122)	(14,198)	(14,236)
Debt retirement costs													(2,338)	0	0
Tax benefit of interest expense and other parent company current tax adjustments													6,829	6,371	6,030
Combined net income													74,514	86,142	86,116
Increase (decrease) due to:
Deferred policy acquisition costs													13,249	16,828	17,177
Policyholder benefits													14,065	15,284	19,038
Federal income tax expense													(6,678)	(10,548)	(12,735)
Investment reserves													7,339	3,574	6,818
Other adjustments, net													(9,007)	(7,037)	(5,521)
Net income as reported herein	$ 21,040	$ 21,984	$ 16,183	$ 34,275	$ 30,068	$ 25,357	$ 20,452	$ 28,366	$ 34,287	$ 23,599	$ 25,995	$ 27,012	$ 93,482	$ 104,243	$ 110,893