Financial Instruments and Concentrations of Risk Financial Instruments Transfers In and Out of Level 3 (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member]
Realized/Unrealized (gain) loss included in earnings	$ (1,100)
Fair Value, Measurements, Recurring [Member]
Net liabilities - beginning balance	1,328
Net liabilities - ending balance	32
Fair Value, Inputs, Level 3 [Member] \| Not Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member]
Net liabilities - beginning balance	0
Interest rate swaps acquired through acquisition (Note 5)	3,275
Transfers out of Level 3	0
Realized/Unrealized (gain) loss included in earnings	(1,124)
Settlements	(923)
Net liabilities - ending balance	1,228
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Net liabilities - beginning balance	0
Net liabilities - ending balance	$ 1,228

Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6405-128476

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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