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		Sep. 30, 2017	Dec. 31, 2016
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		$ 193,931	$ 228,354
Amortized Cost/Cost		196,009	234,647
Gross Unrealized Losses and OTTI	[1]	(2,078)	(6,293)
Less than or equal to six months
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		169,706	189,619
Amortized Cost/Cost		170,672	193,353
Gross Unrealized Losses and OTTI	[1]	(966)	(3,734)
Less than or equal to six months | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		117,891	64,992
Amortized Cost/Cost		118,457	66,625
Gross Unrealized Losses and OTTI	[1]	(566)	(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		10,250	30,729
Amortized Cost/Cost		10,282	31,253
Gross Unrealized Losses and OTTI	[1]	(32)	(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		27,104	30,698
Amortized Cost/Cost		27,393	31,285
Gross Unrealized Losses and OTTI	[1]	(289)	(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		2,092	54,987
Amortized Cost/Cost		2,127	55,690
Gross Unrealized Losses and OTTI	[1]	(35)	(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		6,594
Amortized Cost/Cost		6,622
Gross Unrealized Losses and OTTI	[1]	(28)
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		3,742
Amortized Cost/Cost		3,812
Gross Unrealized Losses and OTTI	[1]	(70)
Less than or equal to six months | Equity AFS securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		5,775
Amortized Cost/Cost		5,791
Gross Unrealized Losses and OTTI	[1]	(16)
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		7,513	6,623
Amortized Cost/Cost		7,832	7,104
Gross Unrealized Losses and OTTI	[1]	(319)	(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		1,219	4,522
Amortized Cost/Cost		1,394	4,863
Gross Unrealized Losses and OTTI	[1]	(175)	(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		1,557	879
Amortized Cost/Cost		1,605	1,000
Gross Unrealized Losses and OTTI	[1]	(48)	(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		995	1,010
Amortized Cost/Cost		1,021	1,012
Gross Unrealized Losses and OTTI	[1]	(26)	(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		16,712	32,112
Amortized Cost/Cost		17,505	34,190
Gross Unrealized Losses and OTTI	[1]	(793)	(2,078)
Greater than one year | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		7,836	19,541
Amortized Cost/Cost		8,489	21,131
Gross Unrealized Losses and OTTI	[1]	(653)	(1,590)
Greater than one year | Fixed maturity AFS securities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		7,986	7,978
Amortized Cost/Cost		8,102	8,182
Gross Unrealized Losses and OTTI	[1]	(116)	(204)
Greater than one year | Fixed maturity AFS securities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		8	2,122
Amortized Cost/Cost		8	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		882	856
Amortized Cost/Cost		906	909
Gross Unrealized Losses and OTTI	[1]	$ (24)	(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).