Derivative Financial Instruments - Notional Values (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	$ 5,200,000
Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	5,177,388	$ 5,495,857
Interest Rate Swaps | Trading
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	494,638	1,305,757
Interest Rate Swaps | Cash Flow | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	1,054,688	1,109,933
Interest Rate Swaps | Fair Value | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	$ 3,628,062	$ 3,080,167