Investments - Schedule of Selected Information about Sales of Fixed Maturities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales	$ 340,434	$ 226,792	$ 109,024
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales	358,285	226,792	109,024
Gross realized gains	6,133	259	17,583
Gross realized losses	(32,608)	$ (16,894)	$ (1,879)
Unsettled sales	$ 18,000