Derivative Instruments Fair Value and Offsets Table (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		$ 200
Derivative Asset, Fair Value, Gross Asset	$ 1,445	575
Derivative Asset, Fair Value, Gross Liability	(543)	(553)
Derivative Asset, Fair Value, Amount Offset Against Collateral	902	22
Derivative Liability, Fair Value, Gross Liability	618	1,973
Derivative Liability, Fair Value, Gross Asset	(543)	(748)
Derivative Liability, Fair Value, Amount Offset Against Collateral	75	1,225
Financial Swaps | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,401	18
Derivative Asset, Fair Value, Gross Liability	(499)	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	902	18
Derivative Liability, Fair Value, Gross Liability	499	0
Derivative Liability, Fair Value, Gross Asset	(499)	0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Financial Swaps | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	36	553
Derivative Asset, Fair Value, Gross Liability	(36)	(553)
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liability, Fair Value, Gross Liability	84	1,971
Derivative Liability, Fair Value, Gross Asset	(36)	(748)	[1]
Derivative Liability, Fair Value, Amount Offset Against Collateral	48	1,223
Financial Swaps | Other Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		4
Derivative Asset, Fair Value, Gross Liability		0
Derivative Asset, Fair Value, Amount Offset Against Collateral		4
Derivative Liability, Fair Value, Gross Liability		0
Derivative Liability, Fair Value, Gross Asset		0
Derivative Liability, Fair Value, Amount Offset Against Collateral		0
Financial Swaps | Other Liabilities
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	8
Derivative Asset, Fair Value, Gross Liability	(8)
Derivative Asset, Fair Value, Amount Offset Against Collateral	0
Derivative Liability, Fair Value, Gross Liability	35
Derivative Liability, Fair Value, Gross Asset	(8)
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 27
Forward contracts | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0
Derivative Asset, Fair Value, Gross Liability		0
Derivative Asset, Fair Value, Amount Offset Against Collateral		0
Derivative Liability, Fair Value, Gross Liability		2
Derivative Liability, Fair Value, Gross Asset		0
Derivative Liability, Fair Value, Amount Offset Against Collateral		$ 2

[1] Current liability derivative amount offset includes $0.2 million of collateral receivable for the period ended December 31, 2017.