Summary of Components of Net Losses and Loss Adjustment Expenses Incurred (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
Insurance [Abstract]
Direct									$ 795,414	$ 703,361	$ 657,059
Assumed									87,995	97,947	118,352
Ceded									(217,961)	(228,710)	(230,182)
Net losses and LAE	$ 172,493	$ 172,793	$ 167,206	$ 152,956	$ 153,881	$ 146,546	$ 141,973	$ 130,198	$ 665,448	$ 572,598	$ 545,229