Variable Interest Entities (Details) - director	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2015
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%
HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured		15.00%
BAM
Variable Interest Entity [Line Items]
Right to elect directors on board number	2
Prospector Offshore Fund
Variable Interest Entity [Line Items]
Ownership of variable interest entity			67.60%
First Loss Reinsurance Treaty | HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%
First Loss Reinsurance Treaty | BAM
Variable Interest Entity [Line Items]
Percentage of premiums	60.00%