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, 2012 Investment	Dec. 31, 2011 Investment
Fixed maturities
Gain (Loss) on Investments [Line Items]
Number of Securities	132	183
Fair Value	$ 187,488	$ 305,121
Gross Unrealized Loss	2,837	10,782
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign government bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	14	9
Fair Value	59,951	65,470
Gross Unrealized Loss	160	383
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign government bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	13	7
Fair Value	55,371	58,587
Gross Unrealized Loss	71	98
Fixed maturities | U.S. Treasury bonds, agency bonds, and foreign government bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	2
Fair Value	4,580	6,883
Gross Unrealized Loss	89	285
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Number of Securities	12	13
Fair Value	8,754	8,530
Gross Unrealized Loss	115	108
Fixed maturities | States, municipalities and political subdivisions | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	7
Fair Value	3,805	5,894
Gross Unrealized Loss	48	72
Fixed maturities | States, municipalities and political subdivisions | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	1
Fair Value	3,369	216
Gross Unrealized Loss	46	1
Fixed maturities | States, municipalities and political subdivisions | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	5
Fair Value	1,580	2,420
Gross Unrealized Loss	21	35
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	2	3
Fair Value	1,683	5,087
Gross Unrealized Loss	44	3
Fixed maturities | Agency mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	3
Fair Value	1,683	5,087
Gross Unrealized Loss	44	3
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Number of Securities	56	60
Fair Value	32,987	22,671
Gross Unrealized Loss	1,651	2,848
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	6
Fair Value	18,163	6,672
Gross Unrealized Loss	56	184
Fixed maturities | Residential Mortgage Backed Securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	7	7
Fair Value	2,673	5,250
Gross Unrealized Loss	88	313
Fixed maturities | Residential Mortgage Backed Securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	48	47
Fair Value	12,151	10,749
Gross Unrealized Loss	1,507	2,351
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	8	8
Fair Value	12,024	11,580
Gross Unrealized Loss	33	75
Fixed maturities | Asset-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	2
Fair Value	7,045	4,933
Gross Unrealized Loss	4	12
Fixed maturities | Asset-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	5
Fair Value	369	6,645
Gross Unrealized Loss	1	63
Fixed maturities | Asset-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	1
Fair Value	4,610	2
Gross Unrealized Loss	28
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	11	12
Fair Value	5,309	13,808
Gross Unrealized Loss	55	593
Fixed maturities | Commercial mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	6
Fair Value	520	5,465
Gross Unrealized Loss	1	29
Fixed maturities | Commercial mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	3
Fair Value	3,754	6,840
Gross Unrealized Loss	43	550
Fixed maturities | Commercial mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	3
Fair Value	1,035	1,503
Gross Unrealized Loss	11	14
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	29	78
Fair Value	66,780	177,975
Gross Unrealized Loss	779	6,772
Fixed maturities | Corporate bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	52
Fair Value	18,246	135,516
Gross Unrealized Loss	47	4,539
Fixed maturities | Corporate bonds | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	16	18
Fair Value	35,128	27,561
Gross Unrealized Loss	443	1,457
Fixed maturities | Corporate bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	10	8
Fair Value	13,406	14,898
Gross Unrealized Loss	289	776
Common Stock
Gain (Loss) on Investments [Line Items]
Number of Securities	2	5
Fair Value	3,119	4,949
Gross Unrealized Loss	517	958
Common Stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	4
Fair Value	1,579	3,320
Gross Unrealized Loss	469	587
Common Stock | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	1
Fair Value	1,540	1,629
Gross Unrealized Loss	$ 48	$ 371