Basis of Presentation and Significant Accounting Policies FX gain (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Foreign Currency Transaction Gain (Loss), before Tax			$ 13,108	$ (3,591)
Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax			23,155	2,011
Premiums Receivable [Member]
Foreign Currency Transaction Gain (Loss), before Tax			(9,783)	512
Loss and Loss Reserves [Member]
Foreign Currency Transaction Gain (Loss), before Tax			(774)	(6,359)
Gain (Loss) on Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ 25,853	$ 6,815	$ 23,155	$ 2,011