Segment Information - Net Premiums (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	$ 2,831,348	$ 2,662,825	$ 2,507,352
Net premiums written	2,654,952	2,514,116	2,458,136
Net premiums earned	$ 2,568,150	$ 2,429,069	$ 2,251,743
% of Total Net premiums written	100.00%	100.00%	100.00%
% of Total Net premiums earned	100.00%	100.00%	100.00%
AmTrust Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	$ 2,006,646	$ 1,885,974	$ 1,610,485
North America
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	2,442,483	2,165,309	1,979,768
Net premiums written	2,280,232	2,038,444	1,934,644
Net premiums earned	2,184,184	2,027,141	1,778,579
Other (predominantly Europe)
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	388,865	497,516	527,584
Net premiums written	374,720	475,672	523,492
Net premiums earned	383,966	401,928	473,164
Operating Segments | Diversified Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	824,341	776,852	897,748
Net premiums written	766,119	734,781	850,049
Net premiums earned	$ 724,124	$ 744,875	$ 854,026
% of Total Net premiums written	28.90%	29.20%	34.60%
% of Total Net premiums earned	28.20%	30.70%	37.90%
Operating Segments | AmTrust Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	$ 2,006,646	$ 1,885,974	$ 1,610,485
Net premiums written	1,888,428	1,779,334	1,610,485
Net premiums earned	$ 1,843,621	$ 1,684,191	$ 1,378,327
% of Total Net premiums written	71.10%	70.80%	65.50%
% of Total Net premiums earned	71.80%	69.30%	61.20%
Operating Segments | Property | Diversified Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 141,353	$ 160,939	$ 160,308
Net premiums earned	$ 136,629	$ 157,186	$ 174,785
% of Total Net premiums written	5.30%	6.40%	6.50%
% of Total Net premiums earned	5.30%	6.50%	7.70%
Operating Segments | Casualty | Diversified Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 466,089	$ 435,625	$ 535,518
Net premiums earned	$ 432,509	$ 449,000	$ 533,775
% of Total Net premiums written	17.60%	17.30%	21.80%
% of Total Net premiums earned	16.80%	18.50%	23.70%
Operating Segments | Accident and Health | Diversified Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 80,004	$ 64,102	$ 38,870
Net premiums earned	$ 74,204	$ 55,672	$ 39,918
% of Total Net premiums written	3.00%	2.60%	1.60%
% of Total Net premiums earned	2.90%	2.30%	1.80%
Operating Segments | International | Diversified Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 78,673	$ 74,115	$ 115,353
Net premiums earned	$ 80,782	$ 83,017	$ 105,548
% of Total Net premiums written	3.00%	2.90%	4.70%
% of Total Net premiums earned	3.20%	3.40%	4.70%
Operating Segments | Small Commercial Business | AmTrust Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 1,181,496	$ 1,057,968	$ 857,576
Net premiums earned	$ 1,131,582	$ 984,333	$ 752,188
% of Total Net premiums written	44.50%	42.10%	34.90%
% of Total Net premiums earned	44.10%	40.50%	33.40%
Operating Segments | Specialty Program | AmTrust Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 344,677	$ 332,416	$ 220,121
Net premiums earned	$ 337,396	$ 290,209	$ 175,286
% of Total Net premiums written	13.00%	13.20%	8.90%
% of Total Net premiums earned	13.10%	11.90%	7.80%
Operating Segments | Specialty Risk and Extended Warranty | AmTrust Reinsurance segment
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 362,255	$ 388,950	$ 532,788
Net premiums earned	$ 374,643	$ 409,649	$ 450,853
% of Total Net premiums written	13.60%	15.50%	21.70%
% of Total Net premiums earned	14.60%	16.90%	20.00%
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Gross premiums written	$ 361	$ (1)	$ (881)
Net premiums written	405	1	(2,398)
Net premiums earned	$ 405	$ 3	$ 19,390
% of Total Net premiums written	0.00%	0.00%	(0.10%)
% of Total Net premiums earned	0.00%	0.00%	0.90%