Schedule II. Condensed Financial Information of Registrant - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Short-term investments	$ 7,718	$ 33,684
Other investments	12,217	11,748
Total investments	1,045,152	1,016,333
Cash and cash equivalents	69,481	90,956	$ 123,077	$ 92,676
Deferred income taxes	29,905	31,231
Property and equipment, net	6,181	7,240
Other assets	42,788	14,287
Total assets	1,502,045	1,457,220
Liabilities:
Accounts payable and other liabilities	30,484	30,110
Total liabilities	1,048,064	1,010,252
Shareholders' equity (net of Treasury stock of $22,370 at December 31, 2015 and 2014)	453,981	446,968	416,814	381,222
Total liabilities and shareholders' equity	1,502,045	1,457,220
Parent Company [Member]
Assets
Short-term investments		250
Other investments	12,217	11,748
Investment in subsidiaries	408,135	387,954
Total investments	420,352	399,952
Cash and cash equivalents	26,968	43,585	$ 47,726	$ 31,792
Deferred income taxes	292	1,001
Notes receivable from subsidiaries	1,505	(1)
Property and equipment, net	1,817	2,070
Other assets	3,047	4,992
Total assets	453,981	451,599
Liabilities:
Accounts payable and other liabilities		3,853
Notes payable to subsidiaries		778
Total liabilities		4,631
Shareholders' equity (net of Treasury stock of $22,370 at December 31, 2015 and 2014)	453,981	446,968
Total liabilities and shareholders' equity	$ 453,981	$ 451,599