Derivative Instruments -Income effects of our cash flow hedging (Details) - Cash Flow Hedging - Designated as Hedging Instruments - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2014
Effects of derivative instruments
Amount of Loss (Gain) Recognized on Derivatives in the Statements of Income	$ (122)	$ (371)
Interest rate contracts \| Interest expense Member
Effects of derivative instruments
Amount of Loss (Gain) Recognized on Derivatives in the Statements of Income	$ (122)	$ (371)

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

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)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a),(c),(d),(e)

-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration