Derivative Financial Instruments - Notional Values (Details) - Interest rate swaps - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Notional values	$ 6,130,763	$ 5,495,857
Trading
Derivatives, Fair Value [Line Items]
Notional values	1,215,900	1,305,757
Cash Flow Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	1,106,847	1,109,933
Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	$ 3,808,016	$ 3,080,167