Derivative Instruments (Gross Notional Amount and Fair Value of Derivatives Contracts) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Assets	$ 317,165	$ 251,768
Liabilities	(74,351)	(97,802)
Derivative, Notional Amount	4,535,457	4,200,893
Derivatives Designated as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	98,055	36,551
Liabilities	(403)	(12,521)
Derivative, Notional Amount	799,428	777,548
Derivatives Designated as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	233	0
Liabilities	0	(50)
Derivative, Notional Amount	3,557	3,615
Derivatives Designated as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	97,822	36,551
Liabilities	(403)	(12,471)
Derivative, Notional Amount	795,871	773,933
Derivatives Not Qualifying as Hedge Accounting Instruments:
Derivative [Line Items]
Assets	219,110	215,217
Liabilities	(73,948)	(85,281)
Derivative, Notional Amount	3,736,029	3,423,345
Derivatives Not Qualifying as Hedge Accounting Instruments: | Interest Rate Swaps
Derivative [Line Items]
Assets	71,613	33,256
Liabilities	(13,849)	(4,490)
Derivative, Notional Amount	568,050	569,925
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Forwards
Derivative [Line Items]
Assets	40	0
Liabilities	(704)	(518)
Derivative, Notional Amount	38,421	21,580
Derivatives Not Qualifying as Hedge Accounting Instruments: | Credit Default Swaps
Derivative [Line Items]
Assets	29	0
Liabilities	0	0
Derivative, Notional Amount	2,313	0
Derivatives Not Qualifying as Hedge Accounting Instruments: | Foreign Currency Swaps
Derivative [Line Items]
Assets	19,336	7,563
Liabilities	(14)	(1,892)
Derivative, Notional Amount	136,770	151,792
Derivatives Not Qualifying as Hedge Accounting Instruments: | Equity Options
Derivative [Line Items]
Assets	128,092	174,398
Liabilities	(59,381)	(78,381)
Derivative, Notional Amount	$ 2,990,475	$ 2,680,048