Schedule III Supplementary Insurance Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Deferred commission and other acquisition expenses	$ 424,605	$ 397,548	$ 372,487
Reserve for loss and loss adjustment expenses	2,896,496	2,510,101	2,271,292
Unearned premiums	1,475,506	1,354,572	1,207,757
Net premiums earned	2,568,150	2,429,069	2,251,743
Net investment income	145,892	131,092	117,215
Net loss and LAE	1,819,906	1,633,570	1,498,271
Amortization of deferred commission and other acquisition expenses	773,664	724,197	659,315
General and admin. expenses	66,984	64,872	62,558
Net premiums written	2,654,952	2,514,116	2,458,136
Operating Segments | Diversified Reinsurance segment
Supplementary Insurance Information, by Segment [Line Items]
Deferred commission and other acquisition expenses	85,432	80,012	87,289
Reserve for loss and loss adjustment expenses	1,103,936	1,046,471	1,058,924
Unearned premiums	323,873	277,460	293,893
Net premiums earned	724,124	744,875	854,026
Net investment income	0	0	0
Net loss and LAE	579,520	547,296	579,771
Amortization of deferred commission and other acquisition expenses	188,506	196,292	233,711
General and admin. expenses	35,681	35,312	38,858
Net premiums written	766,119	734,781	850,049
Operating Segments | AmTrust Reinsurance segment
Supplementary Insurance Information, by Segment [Line Items]
Deferred commission and other acquisition expenses	339,173	317,536	285,232
Reserve for loss and loss adjustment expenses	1,757,728	1,420,418	1,122,479
Unearned premiums	1,151,633	1,077,112	913,861
Net premiums earned	1,843,621	1,684,191	1,378,327
Net investment income	0	0	0
Net loss and LAE	1,225,830	1,074,072	893,502
Amortization of deferred commission and other acquisition expenses	584,820	527,863	418,908
General and admin. expenses	2,896	3,016	2,533
Net premiums written	1,888,428	1,779,334	1,610,485
Operating Segments | Total reportable segments
Supplementary Insurance Information, by Segment [Line Items]
Deferred commission and other acquisition expenses	424,605	397,548	372,521
Reserve for loss and loss adjustment expenses	2,861,664	2,466,889	2,181,403
Unearned premiums	1,475,506	1,354,572	1,207,754
Net premiums earned	2,567,745	2,429,066	2,232,353
Net investment income	0	0	0
Net loss and LAE	1,805,350	1,621,368	1,473,273
Amortization of deferred commission and other acquisition expenses	773,326	724,155	652,619
General and admin. expenses	38,577	38,328	41,391
Net premiums written	2,654,547	2,514,115	2,460,534
Other
Supplementary Insurance Information, by Segment [Line Items]
Deferred commission and other acquisition expenses	0	0	(34)
Reserve for loss and loss adjustment expenses	34,832	43,212	89,889
Unearned premiums	0	0	3
Net premiums earned	405	3	19,390
Net investment income	145,892	131,092	117,215
Net loss and LAE	14,556	12,202	24,998
Amortization of deferred commission and other acquisition expenses	338	42	6,696
General and admin. expenses	28,407	26,544	21,167
Net premiums written	$ 405	$ 1	$ (2,398)