Loss Reserves - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) Segment	Jun. 30, 2016 USD ($)
Insurance [Abstract]
Increase in incurred losses and LAE	$ 26,500
Net prior accident year reserve strengthening	$ 15,115	$ (10,613)
Number of reportable segments | Segment	3
Increase in additional net current AY loss activity	$ 10,900
Increase in losses and loss adjustment expense payments	$ 46,600