Derivative Financial Instruments - Notional Values (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Notional values	$ 5,800,000
Interest rate swaps
Derivatives, Fair Value [Line Items]
Notional values	5,762,829	$ 5,177,388
Interest rate swaps | Trading
Derivatives, Fair Value [Line Items]
Notional values	694,776	494,638
Interest rate swaps | Cash Flow Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	996,458	1,054,688
Interest rate swaps | Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	$ 4,071,595	$ 3,628,062