Summary of Components of Net Written Premium (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Insurance [Abstract]
Direct									$ 1,277,728	$ 1,232,012	$ 1,177,483
Assumed									175,774	200,341	193,034
Ceded written premiums									(409,642)	(432,215)	(482,595)
Net written premiums	$ 244,719	$ 251,939	$ 258,244	$ 288,958	$ 228,007	$ 228,417	$ 231,864	$ 311,850	$ 1,043,860	$ 1,000,138	$ 887,922