Summary of Aggregate Fair Value and Gross Unrealized Loss by Length of Time Securities had Continuously been in Gross Unrealized Loss Position as Well as Number of Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013 Investment	Dec. 31, 2012 Investment
Fixed maturities
Gain (Loss) on Investments [Line Items]
Number of Securities	405	99
Fair Value	$ 934,607	$ 156,071
Gross Unrealized Loss	32,980	1,261
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Number of Securities	53	12
Fair Value	285,730	42,530
Gross Unrealized Loss	8,855	36
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	27	8
Fair Value	136,360	23,760
Gross Unrealized Loss	1,096	22
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	26	3
Fair Value	149,370	14,118
Gross Unrealized Loss	7,759	11
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities		1
Fair Value		4,652
Gross Unrealized Loss		3
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Number of Securities	138	14
Fair Value	257,641	24,207
Gross Unrealized Loss	13,651	380
Fixed maturities | States, municipalities and political subdivisions | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	28	10
Fair Value	40,132	21,299
Gross Unrealized Loss	297	325
Fixed maturities | States, municipalities and political subdivisions | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	104
Fair Value	205,152
Gross Unrealized Loss	12,100
Fixed maturities | States, municipalities and political subdivisions | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	6	4
Fair Value	12,357	2,908
Gross Unrealized Loss	1,254	55
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	112	12
Fair Value	140,102	64,187
Gross Unrealized Loss	6,016	204
Fixed maturities | Agency mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	39	10
Fair Value	39,458	62,516
Gross Unrealized Loss	434	174
Fixed maturities | Agency mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	64	2
Fair Value	77,860	1,671
Gross Unrealized Loss	3,768	30
Fixed maturities | Agency mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	9
Fair Value	22,784
Gross Unrealized Loss	1,814
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Number of Securities	25	41
Fair Value	3,848	9,077
Gross Unrealized Loss	161	549
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	6
Fair Value	431	1,825
Gross Unrealized Loss	2	22
Fixed maturities | Residential Mortgage Backed Securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	7
Fair Value	950
Gross Unrealized Loss	29
Fixed maturities | Residential Mortgage Backed Securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	15	35
Fair Value	2,467	7,252
Gross Unrealized Loss	130	527
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	15	2
Fair Value	76,090	2,369
Gross Unrealized Loss	480	49
Fixed maturities | Asset-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	14
Fair Value	75,887
Gross Unrealized Loss	479
Fixed maturities | Asset-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1
Fair Value	203
Gross Unrealized Loss	1
Fixed maturities | Asset-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities		2
Fair Value		2,369
Gross Unrealized Loss		49
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	10	12
Fair Value	22,584	3,484
Gross Unrealized Loss	374	18
Fixed maturities | Commercial mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	7
Fair Value	6,712	2,639
Gross Unrealized Loss	31	7
Fixed maturities | Commercial mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2
Fair Value	15,098
Gross Unrealized Loss	322
Fixed maturities | Commercial mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	5
Fair Value	774	845
Gross Unrealized Loss	21	11
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	52	6
Fair Value	148,612	10,217
Gross Unrealized Loss	3,443	25
Fixed maturities | Corporate bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	34	2
Fair Value	93,591	3,528
Gross Unrealized Loss	717	6
Fixed maturities | Corporate bonds | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	18
Fair Value	55,021
Gross Unrealized Loss	2,726
Fixed maturities | Corporate bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities		4
Fair Value		6,689
Gross Unrealized Loss		19
Common Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	7	14
Fair Value	10,925	25,288
Gross Unrealized Loss	550	626
Common Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	13
Fair Value	7,387	23,345
Gross Unrealized Loss	422	522
Common Stock | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	1
Fair Value	3,538	1,943
Gross Unrealized Loss	$ 128	$ 104