Investments - Realized Gain (Loss) on Investments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Gain (Loss) on Securities [Line Items]
Realized gains (losses)	$ 5,154	$ 11,813	$ 6,483	$ 13,764
Applicable tax	(1,082)	(2,480)	(1,361)	(2,890)
Realized gains (losses), net of tax	4,072	9,333	5,122	10,874
Fixed maturities available for sale
Gain (Loss) on Securities [Line Items]
Realized gains (losses)	2,237	9,431	5,907	10,817
Fair value option—change in fair value
Gain (Loss) on Securities [Line Items]
Realized gains (losses)	2,869	2,301	684	2,861
Other investments
Gain (Loss) on Securities [Line Items]
Realized gains (losses)	$ 48	$ 81	$ (108)	$ 86