Condensed Financial Information of Registrant (Parent Only) Statement of Operations and Comprehensive Income (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Net investment income		$ 8,880	$ 8,795	$ 6,562	$ 9,746	$ 8,375	$ 8,852	$ 9,141	$ 8,241	$ 33,983	$ 34,609	$ 28,821
Total revenues										534,514	538,778	333,755
Expenses:
Income before income taxes		46,535	10,598	(11,468)	1,953	29,463	(9,727)	9,772	3,238	47,618	32,746	71,194
Equity in earnings of unconsolidated subsidiaries										5,190	2,533	0
Net income		$ 38,373	$ 9,535	$ (5,165)	$ 7,125	$ 27,304	$ (3,746)	$ 11,117	$ 6,794	49,868	41,469	62,856
Other comprehensive income (loss), net of tax:
Unrealized holding losses										10,058	(17,457)	6,878
Other comprehensive income (loss), net of tax										(4,696)	(19,306)	(30,644)
Comprehensive income, net of tax										45,172	22,163	32,212
Parent Company
Revenues:
Net investment income										28
Total revenues										28
Expenses:
Intercompany interest expense	[1]									198	1,296	1,296
Other expenses										1,833	8,203	4,484
Income before income taxes										(2,003)	(9,499)	(5,780)
Equity in earnings of unconsolidated subsidiaries	[1]									51,871	50,968	68,636
Net income										49,868	41,469	62,856
Other comprehensive income (loss), net of tax:
Unrealized holding losses										(17)
Equity in other comprehensive loss of unconsolidated subsidiaries	[1]									(4,679)	(19,306)	(30,644)
Other comprehensive income (loss), net of tax										(4,696)	(19,306)	(30,644)
Comprehensive income, net of tax										$ 45,172	$ 22,163	$ 32,212

[1] This item has been eliminated in the Company's Consolidated Financial Statements.