Financial Derivatives - Schedule of Derivative Instruments, Impact on Results of Operations (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ (1,900)	$ (4,000)	$ (6,900)	$ (12,900)
Gains/(losses) on financial derivatives and hedging activities		661	(1,601)	2,530	(13,079)
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge		166	(10,550)	4,750	35,778
Gain (Loss) on Fair Value Hedges Recognized in Earnings		1,742	726	(716)	5,716
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities		(890)	(2,259)	3,611	(18,473)
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Components Included from Assessment of Interest Rate Fair Value Hedge Effectiveness		1,600	1,000	(700)	4,200
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net		(100)	200	0	(1,500)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	[1]	1,576	11,276	(5,466)	(30,062)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness		(191)	(68)	(365)	(322)
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net		(191)	(68)	(365)	(322)
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities		(1,031)	(2,333)	4,006	(16,820)
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities		0	79	(588)	(789)
Future [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(losses) on financial derivatives and hedging activities		$ 141	$ (5)	$ 193	$ (864)

[1] Included in the assessment of hedge effectiveness as of September 30, 2017, but excluded from the amounts in the table, were losses of $1.6 million and gains of $0.7 million, respectively, for the three and nine months ended September 30, 2017, attributable to the fair value of the swaps at the inception of the hedging relationship. Accordingly, the amounts recognized as hedge ineffectiveness for three and nine months ended September 30, 2017 were gains of $0.1 million and zero, respectively. The comparable amounts as of September 30, 2016 were losses of $1.0 million and $4.2 million for the three and nine months ended September 30, 2016, attributable to the fair value of the swaps at the inception of the hedging relationship and, accordingly, losses of $0.2 million and gains of $1.5 million for the three and nine months ended September 30, 2016, attributable to hedge ineffectiveness.