Financial Derivatives - Schedule of Derivative Instruments, Impact on Results of Operations (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ (1,800)	$ (4,100)	$ (5,000)	$ (8,900)
(Losses)/gains on financial derivatives and hedging activities		(617)	(4,696)	1,869	(11,478)
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		9,988	16,541	4,584	46,329
Gain (Loss) on Fair Value Hedges Recognized in Earnings		1,420	2,101	(2,457)	4,990
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives and hedging activities		(1,891)	(6,692)	4,501	(16,214)
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		1,300	1,800	(2,300)	3,300
Gain (Loss) on Fair Value Hedge Ineffectiveness, Net		(100)	(300)	100	(1,700)
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]	(8,568)	(14,440)	(7,041)	(41,339)
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		(146)	(105)	(175)	(254)
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net		(146)	(105)	(175)	(254)
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives and hedging activities		(1,648)	(6,345)	5,036	(14,487)
Forward Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives and hedging activities		(189)	10	(588)	(868)
Future [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Losses)/gains on financial derivatives and hedging activities		$ (54)	$ (357)	$ 53	$ (859)

[1] Included in the assessment of hedge effectiveness as of June 30, 2017, but excluded from the amounts in the table, were losses of $1.3 million and gains of $2.3 million, respectively, for the three and six months ended June 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 six months ended June 30, 2017 were gains of $0.1 million and losses of 0.1 million, respectively. The comparable amounts as of June 30, 2016 were losses of $1.8 million and $3.3 million for the three and six months ended June 30, 2016, attributable to the fair value of the swaps at the inception of the hedging relationship and, accordingly, gains of $0.3 million and $1.7 million for the three and six months ended June 30, 2016, attributable to hedge ineffectiveness.