Derivative Instruments (Hedges of Net Investments in Foreign Operations) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1]	$ 20,357	$ (17,439)	$ (13,232)	$ 22,862
Currency Swap [Member]
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1]	3,930	(5,877)	(5,563)	11,125
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1]	$ 16,427	$ (11,562)	$ (7,669)	$ 11,737

[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.