Condensed Financial Information - Statement of Income (Detail) (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, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues:
Net investment income	$ 14,254	$ 14,094	$ 14,246	$ 13,657	$ 13,616	$ 13,597	$ 15,777	$ 11,258	$ 56,251	$ 54,248	$ 63,500
Total revenues	248,729	224,970	222,490	221,375	244,629	220,409	215,902	196,976	917,564	877,916	766,385
Expenses:
Call premium on Senior Notes	17,895								17,895
Interest expense	4,351	2,053	2,052	2,051	2,051	2,049	2,049	2,049	10,507	8,198	8,188
Other (income) expense	665	210	915	(618)	599	(789)	(387)	(911)	1,172	(1,488)	(1,229)
Total expenses	228,320	193,880	202,269	200,822	203,342	202,269	194,778	185,791	825,291	786,180	733,651
Income before income taxes	20,409	31,090	20,221	20,553	41,287	18,140	21,124	11,185	92,273	91,736	32,734
Income tax benefit	6,076	9,804	6,284	6,643	13,243	5,225	6,225	3,281	28,807	27,974	7,137
Net income	14,333	21,286	13,937	13,910	28,044	12,915	14,899	7,904	63,466	63,762	25,597
Parent Company
Revenues:
Net investment income									13	341	595
Dividends received from wholly-owned subsidiaries										15,000	45,000
Total revenues									13	15,341	45,595
Expenses:
Call premium on Senior Notes									17,895
Interest expense									10,507	8,198	8,188
Other (income) expense									2	1,749	2,969
Total expenses									28,404	9,947	11,157
Income before income taxes									(28,391)	5,394	34,438
Income tax benefit									(9,886)	(3,332)	(3,635)
Income (loss) before equity in undistributed net income of wholly owned subsidiaries									(18,505)	8,726	38,073
Equity in undistributed net income of wholly-owned subsidiaries									81,971	55,036	(12,476)
Net income									$ 63,466	$ 63,762	$ 25,597