Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Assets	$ 334,977	$ 251,768
Liabilities	(130,443)	(97,802)
Derivative, Notional Amount	4,748,665	4,200,893
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	57,862	36,551
Liabilities	(6,014)	(12,521)
Derivative, Notional Amount	804,595	777,548
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	230	0
Liabilities	0	(50)
Derivative, Notional Amount	3,522	3,615
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	57,632	36,551
Liabilities	(6,014)	(12,471)
Derivative, Notional Amount	801,073	773,933
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	277,115	215,217
Liabilities	(124,429)	(85,281)
Derivative, Notional Amount	3,944,070	3,423,345
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	67,222	33,256
Liabilities	(14,285)	(4,490)
Derivative, Notional Amount	618,050	569,925
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Assets	470	0
Liabilities	(82)	(518)
Derivative, Notional Amount	39,641	21,580
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Assets	31	0
Liabilities	0	0
Derivative, Notional Amount	2,313	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	11,568	7,563
Liabilities	(706)	(1,892)
Derivative, Notional Amount	150,766	151,792
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Assets	197,824	174,398
Liabilities	(109,356)	(78,381)
Derivative, Notional Amount	$ 3,133,300	$ 2,680,048