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, 2012 Investment	Dec. 31, 2011 Investment
Fixed maturities
Gain (Loss) on Investments [Line Items]
Number of Securities	151	183
Fair Value	$ 313,550	$ 305,121
Gross Unrealized Loss	4,072	10,782
Fixed maturities | U.S. Government Treasury bonds, agency bonds and foreign government bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	30	9
Fair Value	180,154	65,470
Gross Unrealized Loss	856	383
Fixed maturities | U.S. Government Treasury bonds, agency bonds and foreign government bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	28	7
Fair Value	173,094	58,587
Gross Unrealized Loss	755	98
Fixed maturities | U.S. Government Treasury bonds, agency bonds and foreign government bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	2
Fair Value	7,060	6,883
Gross Unrealized Loss	101	285
Fixed maturities | States, municipalities and political subdivisions
Gain (Loss) on Investments [Line Items]
Number of Securities	11	13
Fair Value	10,354	8,530
Gross Unrealized Loss	156	108
Fixed maturities | States, municipalities and political subdivisions | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	6	7
Fair Value	6,731	5,894
Gross Unrealized Loss	99	72
Fixed maturities | States, municipalities and political subdivisions | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	1
Fair Value	1,906	216
Gross Unrealized Loss	34	1
Fixed maturities | States, municipalities and political subdivisions | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	5
Fair Value	1,717	2,420
Gross Unrealized Loss	23	35
Fixed maturities | Agency mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	4	3
Fair Value	7,368	5,087
Gross Unrealized Loss	7	3
Fixed maturities | Agency mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	3
Fair Value	7,368	5,087
Gross Unrealized Loss	7	3
Fixed maturities | Residential Mortgage Backed Securities
Gain (Loss) on Investments [Line Items]
Number of Securities	55	60
Fair Value	15,101	22,671
Gross Unrealized Loss	2,009	2,848
Fixed maturities | Residential Mortgage Backed Securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	3	6
Fair Value	787	6,672
Gross Unrealized Loss	100	184
Fixed maturities | Residential Mortgage Backed Securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	5	7
Fair Value	2,534	5,250
Gross Unrealized Loss	101	313
Fixed maturities | Residential Mortgage Backed Securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	47	47
Fair Value	11,780	10,749
Gross Unrealized Loss	1,808	2,351
Fixed maturities | Asset-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	5	8
Fair Value	5,293	11,580
Gross Unrealized Loss	45	75
Fixed maturities | Asset-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities		2
Fair Value		4,933
Gross Unrealized Loss		12
Fixed maturities | Asset-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	4	5
Fair Value	5,291	6,645
Gross Unrealized Loss	45	63
Fixed maturities | Asset-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	1
Fair Value	2	2
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Number of Securities	11	12
Fair Value	10,536	13,808
Gross Unrealized Loss	76	593
Fixed maturities | Commercial mortgage-backed securities | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	7	6
Fair Value	9,311	5,465
Gross Unrealized Loss	45	29
Fixed maturities | Commercial mortgage-backed securities | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	3
Fair Value	185	6,840
Gross Unrealized Loss	6	550
Fixed maturities | Commercial mortgage-backed securities | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	3
Fair Value	1,040	1,503
Gross Unrealized Loss	25	14
Fixed maturities | Corporate bonds
Gain (Loss) on Investments [Line Items]
Number of Securities	35	78
Fair Value	84,744	177,975
Gross Unrealized Loss	923	6,772
Fixed maturities | Corporate bonds | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	9	52
Fair Value	37,306	135,516
Gross Unrealized Loss	138	4,539
Fixed maturities | Corporate bonds | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	20	18
Fair Value	39,538	27,561
Gross Unrealized Loss	575	1,457
Fixed maturities | Corporate bonds | > 12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	6	8
Fair Value	7,900	14,898
Gross Unrealized Loss	210	776
Common stock
Gain (Loss) on Investments [Line Items]
Number of Securities	3	5
Fair Value	5,294	4,949
Gross Unrealized Loss	342	958
Common stock | 0-6 months
Gain (Loss) on Investments [Line Items]
Number of Securities	1	4
Fair Value	2,032	3,320
Gross Unrealized Loss	15	587
Common stock | 7-12 months
Gain (Loss) on Investments [Line Items]
Number of Securities	2	1
Fair Value	3,262	1,629
Gross Unrealized Loss	$ 327	$ 371