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		Mar. 31, 2017	Dec. 31, 2016
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		$ 165,057	$ 228,354
Amortized Cost/Cost		169,094	234,647
Gross Unrealized Losses and OTTI	[1]	(4,037)	(6,293)
Less than or equal to six months
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		131,401	189,619
Amortized Cost/Cost		133,843	193,353
Gross Unrealized Losses and OTTI	[1]	(2,442)	(3,734)
Less than or equal to six months | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		50,468	64,992
Amortized Cost/Cost		52,009	66,625
Gross Unrealized Losses and OTTI	[1]	(1,541)	(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		19,318	30,729
Amortized Cost/Cost		19,615	31,253
Gross Unrealized Losses and OTTI	[1]	(297)	(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		27,320	30,698
Amortized Cost/Cost		27,788	31,285
Gross Unrealized Losses and OTTI	[1]	(468)	(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		19,905	54,987
Amortized Cost/Cost		20,009	55,690
Gross Unrealized Losses and OTTI	[1]	(104)	(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		10,610
Amortized Cost/Cost		10,611
Gross Unrealized Losses and OTTI	[1]	(1)
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		3,780
Amortized Cost/Cost		3,811
Gross Unrealized Losses and OTTI	[1]	(31)
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		3,630	6,623
Amortized Cost/Cost		3,751	7,104
Gross Unrealized Losses and OTTI	[1]	(121)	(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			4,522
Amortized Cost/Cost			4,863
Gross Unrealized Losses and OTTI	[1]		(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		2,879	879
Amortized Cost/Cost		3,000	1,000
Gross Unrealized Losses and OTTI	[1]	(121)	(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		751	1,010
Amortized Cost/Cost		751	1,012
Gross Unrealized Losses and OTTI	[1]	0	(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		30,026	32,112
Amortized Cost/Cost		31,500	34,190
Gross Unrealized Losses and OTTI	[1]	(1,474)	(2,078)
Greater than one year | Fixed maturity AFS securities | Corporate securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		17,183	19,541
Amortized Cost/Cost		18,367	21,131
Gross Unrealized Losses and OTTI	[1]	(1,184)	(1,590)
Greater than one year | Fixed maturity AFS securities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		8,076	7,978
Amortized Cost/Cost		8,154	8,182
Gross Unrealized Losses and OTTI	[1]	(78)	(204)
Greater than one year | Fixed maturity AFS securities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		2,221	2,122
Amortized Cost/Cost		2,275	2,172
Gross Unrealized Losses and OTTI	[1]	(54)	(50)
Greater than one year | Fixed maturity AFS securities | Municipals
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		871	856
Amortized Cost/Cost		908	909
Gross Unrealized Losses and OTTI	[1]	(37)	(53)
Greater than one year | Equity AFS securities | Banking securities
Gain (Loss) on Investments [Line Items]
Estimated Fair Value		1,675	1,615
Amortized Cost/Cost		1,796	1,796
Gross Unrealized Losses and OTTI	[1]	$ (121)	$ (181)

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