Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Assets	$ 234,705	$ 77,890
Liabilities	(49,646)	(26,862)
Derivative, Notional Amount	3,968,518	3,070,256
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	62,876	38,333
Liabilities	(3,766)	(16,638)
Derivative, Notional Amount	763,337	719,476
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	62,876	38,333
Liabilities	(3,766)	(16,638)
Derivative, Notional Amount	763,337	719,476
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	171,829	39,557
Liabilities	(45,880)	(10,224)
Derivative, Notional Amount	3,205,181	2,350,780
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	46,055	15,665
Liabilities	(7,834)	(3,174)
Derivative, Notional Amount	569,925	246,925
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Assets	356	277
Liabilities	(116)	(20)
Derivative, Notional Amount	21,326	23,043
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Assets	0	0
Liabilities	0	(9)
Derivative, Notional Amount	0	756
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	12,308	6,303
Liabilities	(310)	(2,109)
Derivative, Notional Amount	154,207	98,363
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Assets	113,110	17,312
Liabilities	(37,620)	(4,912)
Derivative, Notional Amount	$ 2,459,723	$ 1,981,693