v2.4.0.8
Segments - Net Premiums (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Segment Reporting Information [Line Items]    
Net premiums written $ 709,892 $ 689,059
% of Total Net premiums written 100.00% 100.00%
Net premiums earned 519,230 488,442
% of Total Net premiums earned 100.00% 100.00%
Diversified Reinsurance Segment [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 291,619 267,610
% of Total Net premiums written 41.10% 38.80%
Net premiums earned 199,316 196,249
% of Total Net premiums earned 38.40% 40.20%
Diversified Reinsurance Segment [Member] | Property [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 62,581 69,522
% of Total Net premiums written 8.80% 10.10%
Net premiums earned 40,595 47,547
% of Total Net premiums earned 7.80% 9.70%
Diversified Reinsurance Segment [Member] | Casualty [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 171,754 148,423
% of Total Net premiums written 24.20% 21.50%
Net premiums earned 121,887 117,059
% of Total Net premiums earned 23.50% 24.00%
Diversified Reinsurance Segment [Member] | Accident and Health [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 17,222 15,529
% of Total Net premiums written 2.40% 2.20%
Net premiums earned 8,886 8,633
% of Total Net premiums earned 1.70% 1.80%
Diversified Reinsurance Segment [Member] | International [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 40,062 34,136
% of Total Net premiums written 5.70% 5.00%
Net premiums earned 27,948 23,010
% of Total Net premiums earned 5.40% 4.70%
AmTrust Quota Share Reinsurance Segment [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 419,010 344,818
% of Total Net premiums written 59.00% 50.10%
Net premiums earned 304,922 220,288
% of Total Net premiums earned 58.70% 45.00%
AmTrust Quota Share Reinsurance Segment [Member] | Small Commercial Business [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 253,757 162,018
% of Total Net premiums written 35.70% 23.50%
Net premiums earned 158,605 102,257
% of Total Net premiums earned 30.50% 20.90%
AmTrust Quota Share Reinsurance Segment [Member] | Specialty Program [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 31,798 34,946
% of Total Net premiums written 4.50% 5.10%
Net premiums earned 32,853 33,346
% of Total Net premiums earned 6.30% 6.80%
AmTrust Quota Share Reinsurance Segment [Member] | Specialty Risk and Extended Warranty [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written 133,455 147,854
% of Total Net premiums written 18.80% 21.50%
Net premiums earned 113,464 84,685
% of Total Net premiums earned 21.90% 17.30%
NGHC Quota Share Segment [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written (737) 76,631
% of Total Net premiums written (0.10%) 11.10%
Net premiums earned 14,992 71,905
% of Total Net premiums earned 2.90% 14.80%
NGHC Quota Share Segment [Member] | Automobile Liability [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written (534) 44,339
% of Total Net premiums written (0.10%) 6.40%
Net premiums earned 9,096 41,630
% of Total Net premiums earned 1.80% 8.60%
NGHC Quota Share Segment [Member] | Automobile Physical Damage [Member]
    
Segment Reporting Information [Line Items]    
Net premiums written (203) 32,292
% of Total Net premiums written 0.00% 4.70%
Net premiums earned $ 5,896 $ 30,275
% of Total Net premiums earned 1.10% 6.20%