Loss Reserves - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Insurance [Abstract]
Increase in incurred losses and LAE	$ 16,600
Increase in net prior accident year reserve strengthening	8,900
Additional net current AY loss activity	4,900
Net prior AY reserve strengthening	7,085	$ (1,834)
Increase in additional net current AY loss activity	$ 2,500