Derivative Financial Instruments - Notional Values (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional values	$ 5,900,000
Interest rate swaps
Derivatives, Fair Value [Line Items]
Notional values	5,887,127	$ 5,177,388
Interest rate swaps | Trading
Derivatives, Fair Value [Line Items]
Notional values	966,542	494,638
Interest rate swaps | Cash Flow Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	1,440,220	1,054,688
Interest rate swaps | Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	$ 3,480,365	$ 3,628,062