Estimated Fair Value and Gross Unrealized Losses and Other-Than-Temporary Impairments related to Fixed Maturity and Equity Available-for-Sale Securities in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		$ 113,560	$ 228,354
Amortized Cost/Cost		115,688	234,647
Gross Unrealized Losses and OTTI	[1]	(2,128)	(6,293)
Less than or equal to six months
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		54,658	189,619
Amortized Cost/Cost		54,957	193,353
Gross Unrealized Losses and OTTI	[1]	(299)	(3,734)
Less than or equal to six months | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		3,212	64,992
Amortized Cost/Cost		3,288	66,625
Gross Unrealized Losses and OTTI	[1]	(76)	(1,633)
Less than or equal to six months | Fixed maturity AFS securities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		21,820	30,729
Amortized Cost/Cost		21,842	31,253
Gross Unrealized Losses and OTTI	[1]	(22)	(524)
Less than or equal to six months | Fixed maturity AFS securities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		10,578	30,698
Amortized Cost/Cost		10,678	31,285
Gross Unrealized Losses and OTTI	[1]	(100)	(587)
Less than or equal to six months | Fixed maturity AFS securities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		2,880	54,987
Amortized Cost/Cost		2,924	55,690
Gross Unrealized Losses and OTTI	[1]	(44)	(703)
Less than or equal to six months | Fixed maturity AFS securities | Government and government agencies - United States
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		6,593
Amortized Cost/Cost		6,623
Gross Unrealized Losses and OTTI	[1]	(30)
Less than or equal to six months | Fixed maturity AFS securities | Government and government agencies - Foreign
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		3,789
Amortized Cost/Cost		3,811
Gross Unrealized Losses and OTTI	[1]	(22)
Less than or equal to six months | Equity AFS securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		5,786
Amortized Cost/Cost		5,791
Gross Unrealized Losses and OTTI	[1]	(5)
Less than or equal to six months | Equity AFS securities | Banking securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value			8,213
Amortized Cost/Cost			8,500
Gross Unrealized Losses and OTTI	[1]		(287)
Greater than six months but less than or equal to one year
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		39,639	6,623
Amortized Cost/Cost		40,199	7,104
Gross Unrealized Losses and OTTI	[1]	(560)	(481)
Greater than six months but less than or equal to one year | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		19,522	4,522
Amortized Cost/Cost		19,832	4,863
Gross Unrealized Losses and OTTI	[1]	(310)	(341)
Greater than six months but less than or equal to one year | Fixed maturity AFS securities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		6,948	879
Amortized Cost/Cost		7,051	1,000
Gross Unrealized Losses and OTTI	[1]	(103)	(121)
Greater than six months but less than or equal to one year | Fixed maturity AFS securities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		13,169	1,010
Amortized Cost/Cost		13,316	1,012
Gross Unrealized Losses and OTTI	[1]	(147)	(2)
Greater than six months but less than or equal to one year | Fixed maturity AFS securities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value			212
Amortized Cost/Cost			229
Gross Unrealized Losses and OTTI	[1]		(17)
Greater than one year
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		19,263	32,112
Amortized Cost/Cost		20,532	34,190
Gross Unrealized Losses and OTTI	[1]	(1,269)	(2,078)
Greater than one year | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		9,383	19,541
Amortized Cost/Cost		10,489	21,131
Gross Unrealized Losses and OTTI	[1]	(1,106)	(1,590)
Greater than one year | Fixed maturity AFS securities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		8,997	7,978
Amortized Cost/Cost		9,127	8,182
Gross Unrealized Losses and OTTI	[1]	(130)	(204)
Greater than one year | Fixed maturity AFS securities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		9	2,122
Amortized Cost/Cost		9	2,172
Gross Unrealized Losses and OTTI	[1]		(50)
Greater than one year | Fixed maturity AFS securities | Municipals
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		874	856
Amortized Cost/Cost		907	909
Gross Unrealized Losses and OTTI	[1]	$ (33)	(53)
Greater than one year | Equity AFS securities | Banking securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value			1,615
Amortized Cost/Cost			1,796
Gross Unrealized Losses and OTTI	[1]		$ (181)

[1] Subsequent unrealized gains (losses) on OTTI securities are included in Net unrealized OTTI on securities in the Statements of Comprehensive Income (Loss).