Statutory Information and Restrictions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statutory Information and Restrictions [Line Items]
Statutory capital and surplus of insurance subsidiaries	$ 861,421				$ 809,241								$ 861,421	$ 809,241
Increase (decrease) due to:
Deferred policy acquisition costs	215,082				245,355								215,082	245,355
Difference in policyholder reserves	87,345				80,459								87,345	80,459
Goodwill	47,396				47,396								47,396	47,396
Liability for postretirement benefits other than pensions	0				(1,130)								0	(1,130)
Investment fair value adjustments on fixed maturities	519,593				227,060								519,593	227,060
Difference in investment reserves	118,633				111,983								118,633	111,983
Federal income tax liability	(290,034)				(188,426)								(290,034)	(188,426)
Net funded status of pension and other postretirement benefit obligations	(20,027)				(18,217)								(20,027)	(18,217)
Non-admitted assets and other, net	18,528				11,349								18,528	11,349
Shareholders' equity of parent company and non-insurance subsidiaries	16,465				12,109								16,465	12,109
Parent company short-term and long-term debt	(237,939)				(237,874)								(237,939)	(237,874)
Total shareholders' equity	1,336,463				1,099,305				1,245,803				1,336,463	1,099,305	1,245,803
Statutory net income of insurance subsidiaries													97,875	98,905	93,299
Net loss of non-insurance companies													(3,906)	(4,583)	(4,726)
Interest expense													(14,198)	(14,236)	(14,249)
Tax benefit of interest expense and other parent company current tax adjustments													6,371	6,030	9,308
Combined net income													86,142	86,116	83,632
Increase (decrease) due to:
Deferred policy acquisition costs													16,828	17,177	16,595
Policyholder benefits													15,284	19,038	15,574
Federal income tax expense													(10,548)	(12,735)	(19,843)
Investment reserves													3,574	6,818	14,021
Other adjustments, net													(7,037)	(5,521)	(6,113)
Net income as reported herein	$ 30,068	$ 25,357	$ 20,452	$ 28,366	$ 34,287	$ 23,599	$ 25,995	$ 27,012	$ 31,826	$ 32,266	$ 13,103	$ 26,671	$ 104,243	$ 110,893	$ 103,866