v2.4.0.6
Trust Preferred Securities (Detail) (USD $)
In Thousands, unless otherwise specified
 6 Months Ended
Jun. 30, 2012
Dec. 31, 2011
Debt Instrument [Line Items]    
Aggregate Liquidation Amount of Trust Preferred Securities $ 120,000  
Aggregate Liquidation Amount of Common Securities 3,714  
Aggregate Principal Amount of Notes 123,714 123,714
Stated Maturity of Notes Dec. 15, 2021  
Per Annum Interest Rate of Notes 5.50%  
AmTrust Capital Financing Trust I
    
Debt Instrument [Line Items]    
Aggregate Liquidation Amount of Trust Preferred Securities 25,000  
Aggregate Liquidation Amount of Common Securities 774  
Aggregate Principal Amount of Notes 25,774  
Stated Maturity of Notes Mar. 17, 2035  
Per Annum Interest Rate of Notes 8.275% [1]  
AmTrust Capital Financing Trust II
    
Debt Instrument [Line Items]    
Aggregate Liquidation Amount of Trust Preferred Securities 25,000  
Aggregate Liquidation Amount of Common Securities 774  
Aggregate Principal Amount of Notes 25,774  
Stated Maturity of Notes Jun. 15, 2035  
Per Annum Interest Rate of Notes 7.71% [1]  
AmTrust Capital Financing Trust III
    
Debt Instrument [Line Items]    
Aggregate Liquidation Amount of Trust Preferred Securities 30,000  
Aggregate Liquidation Amount of Common Securities 928  
Aggregate Principal Amount of Notes 30,928  
Stated Maturity of Notes Sep. 15, 2036  
Per Annum Interest Rate of Notes 3.768% [2]  
AmTrust Capital Financing Trust IV
    
Debt Instrument [Line Items]    
Aggregate Liquidation Amount of Trust Preferred Securities 40,000  
Aggregate Liquidation Amount of Common Securities 1,238  
Aggregate Principal Amount of Notes $ 41,238  
Stated Maturity of Notes Mar. 15, 2037  
Per Annum Interest Rate of Notes 3.468% [3]  
[1] The interest rate will change to three-month LIBOR plus 3.40% after the tenth anniversary in 2015.
[2] The interest rate is LIBOR plus 3.30%.
[3] The interest rate is LIBOR plus 3.00%.