Schedule II. Condensed Financial Information of Registrant - Condensed Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Short-term investments	$ 33,684	$ 84,422
Fixed-maturity securities-available-for-sale, at fair value	331,242	237,877
Other investments	11,748	10,591
Total investments	1,016,333	878,775
Cash and cash equivalents	90,956	123,077	92,676	45,536
Deferred income taxes	31,231	33,645
Property and equipment, net	7,240	7,549
Other assets	14,287	8,637
Total assets	1,457,220	1,329,001
Liabilities:
Accounts payable and other liabilities	30,110	26,940
Total liabilities	1,010,252	912,187
Shareholders' equity (net of Treasury stock of $22,370 at December 31, 2014 and 2013)	446,968	416,814	381,222	349,437
Total liabilities and shareholders' equity	1,457,220	1,329,001
Parent Company [Member]
Assets
Short-term investments	250	248
Fixed-maturity securities-available-for-sale, at fair value		965
Other investments	11,748	10,591
Investment in subsidiaries	387,954	352,193
Total investments	399,952	363,997
Cash and cash equivalents	43,585	47,726	31,792	14,887
Deferred income taxes	1,001	1,383
Notes receivable from subsidiaries	(1)	1,805
Property and equipment, net	2,070	2,181
Other assets	4,992	556
Total assets	451,599	417,648
Liabilities:
Accounts payable and other liabilities	3,853	834
Notes payable to subsidiaries	778
Total liabilities	4,631	834
Shareholders' equity (net of Treasury stock of $22,370 at December 31, 2014 and 2013)	446,968	416,814
Total liabilities and shareholders' equity	$ 451,599	$ 417,648