Schedule of Investment 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
Schedule of Available-for-sale Securities [Line Items]
Investment income										$ 39,151	$ 37,918	$ 32,420
Investment expense	[1]									(5,168)	(3,309)	(3,599)
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
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Investment income										30,337	32,091	26,788
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Investment income										3,302	3,125	5,484
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Investment income										217	82	61
Other Invested Assets
Schedule of Available-for-sale Securities [Line Items]
Investment income										$ 5,295	$ 2,620	$ 87

[1] Investment expense for the year ended December 31, 2016 includes $1.5 million in upfront fees necessary to enter into a new investment. See Note 9 for additional information on the Company's $40 million commitment related to this new investment.