Derivative Instruments (Hedges of Net Investments in Foreign Operations) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1],[2]	$ 19,260	$ (13,761)	$ 40,301	$ (21,367)
Currency Swap [Member]
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1],[2]	8,197	(17,919)	17,002	(25,525)
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Net Derivatives Gains (Losses) Deferred in AOCI	[1],[2]	$ 11,063	$ 4,158	$ 23,299	$ 4,158

[1] There was no ineffectiveness recognized for the Company’s hedges of net investments in foreign operations.

[2] 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.