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	Jun. 30, 2014 Investment	Dec. 31, 2013 Investment
Fixed maturities
Gain (Loss) on Investments [Line Items]
Number of Securities	271	405
Fair Value	$ 645,099	$ 934,607
Gross Unrealized Loss	10,747	32,980
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign
Gain (Loss) on Investments [Line Items]
Number of Securities	51	53
Fair Value	192,013	285,730
Gross Unrealized Loss	4,339	8,855
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	27
Fair Value	15,576	136,360
Gross Unrealized Loss	13	1,096
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	9	26
Fair Value	22,215	149,370
Gross Unrealized Loss	171	7,759
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	38
Fair Value	154,222
Gross Unrealized Loss	4,155
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Number of Securities	91	138
Fair Value	184,215	257,641
Gross Unrealized Loss	2,883	13,651
Fixed maturities | States, municipalities and political subdivisions | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	17	28
Fair Value	25,239	40,132
Gross Unrealized Loss	158	297
Fixed maturities | States, municipalities and political subdivisions | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	104
Fair Value	3,897	205,152
Gross Unrealized Loss	59	12,100
Fixed maturities | States, municipalities and political subdivisions | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	71	6
Fair Value	155,079	12,357
Gross Unrealized Loss	2,666	1,254
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	63	112
Fair Value	78,883	140,102
Gross Unrealized Loss	1,753	6,016
Fixed maturities | Agency mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	39
Fair Value	1,778	39,458
Gross Unrealized Loss	7	434
Fixed maturities | Agency mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities		64
Fair Value		77,860
Gross Unrealized Loss		3,768
Fixed maturities | Agency mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	61	9
Fair Value	77,105	22,784
Gross Unrealized Loss	1,746	1,814
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Number of Securities	21	25
Fair Value	3,696	3,848
Gross Unrealized Loss	101	161
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	3
Fair Value	1,192	431
Gross Unrealized Loss	6	2
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	16	15
Fair Value	2,504	2,467
Gross Unrealized Loss	95	130
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	8	15
Fair Value	55,698	76,090
Gross Unrealized Loss	381	480
Fixed maturities | Asset-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	14
Fair Value	20,791	75,887
Gross Unrealized Loss	24	479
Fixed maturities | Asset-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	1
Fair Value	34,907	203
Gross Unrealized Loss	357	1
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	6	10
Fair Value	17,135	22,584
Gross Unrealized Loss	131	374
Fixed maturities | Commercial mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	4
Fair Value	1,504	6,712
Gross Unrealized Loss	1	31
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	4
Fair Value	15,631	774
Gross Unrealized Loss	130	21
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	31	52
Fair Value	113,459	148,612
Gross Unrealized Loss	1,159	3,443
Fixed maturities | Corporate bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	14	34
Fair Value	67,019	93,591
Gross Unrealized Loss	197	717
Fixed maturities | Corporate bonds | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	18
Fair Value	6,192	55,021
Gross Unrealized Loss	33	2,726
Fixed maturities | Corporate bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	12
Fair Value	40,248
Gross Unrealized Loss	929
Common Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	7	7
Fair Value	14,138	10,925
Gross Unrealized Loss	964	550
Common Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	5
Fair Value	13,762	7,387
Gross Unrealized Loss	929	422
Common Stock | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	2
Fair Value	376	3,538
Gross Unrealized Loss	35	128
Preferred Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	4
Fair Value	3,294
Gross Unrealized Loss	23
Preferred Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4
Fair Value	3,294
Gross Unrealized Loss	$ 23