Derivative Financial Instruments - Notional Values (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional values	$ 6,200,000
Interest rate swaps
Derivatives, Fair Value [Line Items]
Notional values	6,215,913	$ 5,996,310
Interest rate swaps | Trading
Derivatives, Fair Value [Line Items]
Notional values	1,521,234	1,577,978
Interest rate swaps | Cash Flow Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	1,248,190	1,280,367
Interest rate swaps | Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	$ 3,446,489	$ 3,137,965