Segment Information - Net Premiums (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 10,372	$ (561,530)
Net premiums earned	$ 31,215	$ 183,102
Net premiums earned % of total	100.00%	100.00%
Operating segments | Diversified Reinsurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 10,372	$ 14,947
Net premiums earned	$ 12,531	$ 25,292
Net premiums earned % of total	40.10%	13.80%
Operating segments | Diversified Reinsurance | International
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 10,372	$ 14,947
Net premiums earned	$ 12,531	$ 25,292
Net premiums earned % of total	40.10%	13.80%
Operating segments | AmTrust Reinsurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 0	$ (576,477)
Net premiums earned	$ 18,684	$ 157,810
Net premiums earned % of total	59.90%	86.20%
Operating segments | AmTrust Reinsurance | Small Commercial Business
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 0	$ (342,681)
Net premiums earned	$ 939	$ 39,455
Net premiums earned % of total	3.00%	21.60%
Operating segments | AmTrust Reinsurance | Specialty Program
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 0	$ (12,608)
Net premiums earned	$ 75	$ 76,221
Net premiums earned % of total	0.30%	41.60%
Operating segments | AmTrust Reinsurance | Specialty Risk and Extended Warranty
Segment Reporting, Revenue Reconciling Item [Line Items]
Net premiums written	$ 0	$ (221,188)
Net premiums earned	$ 17,670	$ 42,134
Net premiums earned % of total	56.60%	23.00%