Segment Information (Narrative) (Details)	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Workers' Compensation Insurance
Segment Reporting Information [Line Items]
Worker's compensation SPC percentage ceded	100.00%
Syndicate 1729
Segment Reporting Information [Line Items]
Proportion of capital provided to support Lloyd's Syndicate 1729		61.00%	62.00%
Syndicate 6131
Segment Reporting Information [Line Items]
Proportion of capital provided to support Lloyd's Syndicate 1729				100.00%