Components of Net Realized Investment Gains (Losses) (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Securities, Available-for-sale [Line Items]
Total net realized investment gains (losses)		$ (2,690)	$ 5,319	$ 11,290	$ 7,833
Equity securities, Gross realized gains		1,681	5,789	26,936	12,116
Equity securities, Gross realized losses		(3,146)	(946)	(9,076)	(9,582)
Equity securities, Total net realized investment gains (losses)		(1,465)	4,843	17,860	2,534
Not Designated as Hedging Instrument | Interest Rate Swap
Debt Securities, Available-for-sale [Line Items]
Gross realized gains		341	1,690	341	8,457
Gross realized losses		(2,512)	(379)	(9,745)	(1,498)
Total net realized investment gains (losses)	[1]	(2,171)	1,311	(9,404)	6,959
Fixed Maturities
Debt Securities, Available-for-sale [Line Items]
Gross realized gains		1,054	329	5,765	373
Gross realized losses		(108)	(1,164)	(2,931)	(2,033)
Total net realized investment gains (losses)		$ 946	$ (835)	$ 2,834	$ (1,660)

[1] Includes periodic net interest settlements related to the derivatives of $0.3 million and $0.4 million for the quarters ended September 30, 2019 and 2018, respectively, and $0.7 million and $1.5 million for the nine months ended September 30, 2019 and 2018, respectively.