Derivative Instruments (Details 2) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional Amount		$ 204,000	$ 186,100
Fair Value		9,932	8,694
Bank of America, N.A. [Member]
Derivative [Line Items]
Notional Amount		25,200	38,500
Fair Value		601	1,934
Credit Suisse International [Member]
Derivative [Line Items]
Notional Amount		57,700	65,200
Fair Value		5,164	4,281
Societe Generale [Member]
Derivative [Line Items]
Notional Amount		40,200	15,600
Fair Value		1,835	936
Barclays Bank PLC [Member]
Derivative [Line Items]
Notional Amount		80,900	66,800
Fair Value		2,332	1,543
Citigroup Inc [Member]
Derivative [Line Items]
Notional Amount		0	0
Fair Value		$ 0	$ 0
Moody's [Member] | Bank of America, N.A. [Member]
Derivative [Line Items]
Credit Rating	[1]	A1
Moody's [Member] | Societe Generale [Member]
Derivative [Line Items]
Credit Rating	[1]	A2
Moody's [Member] | Barclays Bank PLC [Member]
Derivative [Line Items]
Credit Rating	[1]	A1
Moody's [Member] | Credit Suisse International [Member]
Derivative [Line Items]
Credit Rating	[1]	A1
Moody's [Member] | Citigroup Inc [Member]
Derivative [Line Items]
Credit Rating	[1]	Baa1
Standard & Poor's [Member] | Bank of America, N.A. [Member]
Derivative [Line Items]
Credit Rating	[1]	A+
Standard & Poor's [Member] | Credit Suisse International [Member]
Derivative [Line Items]
Credit Rating	[1]	A
Standard & Poor's [Member] | Societe Generale [Member]
Derivative [Line Items]
Credit Rating	[1]	A
Standard & Poor's [Member] | Barclays Bank PLC [Member]
Derivative [Line Items]
Credit Rating	[1]	A-
Standard & Poor's [Member] | Citigroup Inc [Member]
Derivative [Line Items]
Credit Rating	[1]	BBB+

[1] As assigned by Standard & Poor’s Corporation (“S&P”) and Moody’s Investors Service, Inc. (“Moody’s”).