Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	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, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summarized financial information for these segments
Insurance premiums and contract charges earned													$ 690,938	$ 670,527	$ 667,120
Net investment income													313,610	306,003	288,311
Net income	34,287	23,599	25,995	27,012	31,826	32,266	13,103	26,671	32,913	23,637	(11,851)	25,807	110,893	103,866	70,506
Assets	8,826,672				8,167,726				7,435,169				8,826,672	8,167,726	7,435,169
Property and casualty [Member]
Summarized financial information for these segments
Insurance premiums and contract charges earned													561,954	546,339	547,540
Net investment income													36,208	36,792	36,886
Net income													44,433	37,043	5,844
Assets	1,001,561				1,016,368				957,266				1,001,561	1,016,368	957,266
Annuity [Member]
Summarized financial information for these segments
Insurance premiums and contract charges earned													22,575	21,794	18,883
Net investment income													208,419	200,785	182,806
Net income													44,719	40,527	30,906
Assets	5,963,348				5,380,780				4,926,204				5,963,348	5,380,780	4,926,204
Life [Member]
Summarized financial information for these segments
Insurance premiums and contract charges earned													106,409	102,394	100,697
Net investment income													69,932	69,409	69,633
Net income													20,339	21,912	19,435
Assets	1,743,084				1,663,696				1,459,919				1,743,084	1,663,696	1,459,919
Corporate and other [Member]
Summarized financial information for these segments
Net investment income													7	2	(3)
Net income													1,402	4,384	14,321
Assets	154,557				131,449				115,367				154,557	131,449	115,367
Intersegment eliminations [Member]
Summarized financial information for these segments
Net investment income													(956)	(985)	(1,011)
Assets	$ (35,878)				$ (24,567)				$ (23,587)				$ (35,878)	$ (24,567)	$ (23,587)