Derivative Instruments (Hedges of Net Investments in Foreign Operations) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1]	$ (8,470)	$ 19,260	$ (33,588)	$ 40,301
Currency Swap [Member]
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1]	(2,486)	8,197	(9,493)	17,002
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1]	$ (5,984)	$ 11,063	$ (24,095)	$ 23,299

[1] There were no sales or substantial liquidations of net investments in foreign operations that would have required the reclassification of gains or losses from accumulated other comprehensive income (loss) into investment income during the periods presented.