Derivative Financial Instruments - Impact of Derivatives on Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 812	$ 7,808
Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Derivative Assets	812	7,808
Derivative Liabilities	(2,584)	(25,937)
Total net derivatives	(1,772)	(18,129)
Trading | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Derivative Assets	182	0
Derivative Liabilities	0	(1,076)
Total net derivatives	182	(1,076)
Cash Flow | Designated as Hedging Instrument | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	(2,584)	(14,463)
Total net derivatives	(2,584)	(14,463)
Fair Value | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Total net derivatives	19,800	30,000
Fair Value | Designated as Hedging Instrument | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Derivative Assets	630	7,808
Derivative Liabilities	0	(10,398)
Total net derivatives	$ 630	$ (2,590)