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	Mar. 31, 2014 Investment	Dec. 31, 2013 Investment
Fixed maturities
Gain (Loss) on Investments [Line Items]
Number of Securities	313	405
Fair Value	$ 899,012	$ 934,607
Gross Unrealized Loss	18,719	32,980
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Number of Securities	42	53
Fair Value	249,442	285,730
Gross Unrealized Loss	4,956	8,855
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	20	27
Fair Value	120,036	136,360
Gross Unrealized Loss	518	1,096
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	21	26
Fair Value	128,509	149,370
Gross Unrealized Loss	4,426	7,759
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1
Fair Value	897
Gross Unrealized Loss	12
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Number of Securities	107	138
Fair Value	221,178	257,641
Gross Unrealized Loss	6,948	13,651
Fixed maturities | States, municipalities and political subdivisions | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	14	28
Fair Value	24,744	40,132
Gross Unrealized Loss	163	297
Fixed maturities | States, municipalities and political subdivisions | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	77	104
Fair Value	160,382	205,152
Gross Unrealized Loss	5,050	12,100
Fixed maturities | States, municipalities and political subdivisions | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	16	6
Fair Value	36,052	12,357
Gross Unrealized Loss	1,735	1,254
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	70	112
Fair Value	106,539	140,102
Gross Unrealized Loss	3,525	6,016
Fixed maturities | Agency mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	6	39
Fair Value	22,200	39,458
Gross Unrealized Loss	65	434
Fixed maturities | Agency mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	53	64
Fair Value	61,847	77,860
Gross Unrealized Loss	2,060	3,768
Fixed maturities | Agency mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	11	9
Fair Value	22,492	22,784
Gross Unrealized Loss	1,400	1,814
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Number of Securities	19	25
Fair Value	3,655	3,848
Gross Unrealized Loss	136	161
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	3
Fair Value	897	431
Gross Unrealized Loss	3	2
Fixed maturities | Residential Mortgage Backed Securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	7
Fair Value	536	950
Gross Unrealized Loss	18	29
Fixed maturities | Residential Mortgage Backed Securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	13	15
Fair Value	2,222	2,467
Gross Unrealized Loss	115	130
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	10	15
Fair Value	73,708	76,090
Gross Unrealized Loss	563	480
Fixed maturities | Asset-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	7	14
Fair Value	42,213	75,887
Gross Unrealized Loss	67	479
Fixed maturities | Asset-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	1
Fair Value	31,495	203
Gross Unrealized Loss	496	1
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	7	10
Fair Value	21,626	22,584
Gross Unrealized Loss	272	374
Fixed maturities | Commercial mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	4
Fair Value	6,103	6,712
Gross Unrealized Loss	13	31
Fixed maturities | Commercial mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	2
Fair Value	15,004	15,098
Gross Unrealized Loss	250	322
Fixed maturities | Commercial mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	4
Fair Value	519	774
Gross Unrealized Loss	9	21
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	58	52
Fair Value	222,864	148,612
Gross Unrealized Loss	2,319	3,443
Fixed maturities | Corporate bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	45	34
Fair Value	176,120	93,591
Gross Unrealized Loss	744	717
Fixed maturities | Corporate bonds | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	12	18
Fair Value	45,043	55,021
Gross Unrealized Loss	1,575	2,726
Fixed maturities | Corporate bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1
Fair Value	1,701
Common Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	13	7
Fair Value	25,372	10,925
Gross Unrealized Loss	1,271	550
Common Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	10	5
Fair Value	21,578	7,387
Gross Unrealized Loss	1,120	422
Common Stock | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	2
Fair Value	3,794	3,538
Gross Unrealized Loss	151	128
Preferred Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	1
Fair Value	553
Gross Unrealized Loss	1
Preferred Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1
Fair Value	553
Gross Unrealized Loss	$ 1