Basis of Presentation and Significant Accounting Policies FX gain (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Foreign Currency Transaction Gain (Loss), before Tax			$ 19,368	$ (5,211)
Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax			29,998	3,474
Premiums Receivable [Member]
Foreign Currency Transaction Gain (Loss), before Tax			(10,127)	815
Loss and Loss Reserves [Member]
Foreign Currency Transaction Gain (Loss), before Tax			(1,017)	(9,549)
Gain (Loss) on Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ 6,843	$ 1,463	$ 29,998	$ 3,474