Derivative Instruments (Details 2) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional Amount		$ 186,100	$ 134,700
Fair Value		8,694	2,501
Bank of America, N.A. [Member]
Derivative [Line Items]
Notional Amount		38,500	17,000
Fair Value		1,934	5
Credit Suisse International [Member]
Derivative [Line Items]
Notional Amount		65,200	12,000
Fair Value		4,281	167
Societe Generale [Member]
Derivative [Line Items]
Notional Amount		15,600	80,800
Fair Value		936	1,347
Barclays Bank PLC [Member]
Derivative [Line Items]
Notional Amount		66,800	7,600
Fair Value		1,543	137
Citigroup Inc [Member]
Derivative [Line Items]
Notional Amount		0	17,300
Fair Value		$ 0	$ 845
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”).