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Derivative Instruments - Cash flow hedges (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Effects of derivative instruments |  |  |  |
Amount of Gain Recognized in OCI on Derivatives (Effective Portion) | $ (433) | $ (112) | $ 1,183 | $ 323
Cash Flow Hedging |  |  |  |
Effects of derivative instruments |  |  |  |
Amount of Gain Recognized in OCI on Derivatives (Effective Portion) | 384 | (338) | 1,415 | (3)
Amount of Loss (Gain) Reclassified from Accumulated OCI into Income (Effective Portion) | (94) | 174 | (69) | 400
Cash Flow Hedging | Interest rate contracts | Interest expense Member |  |  |  |
Effects of derivative instruments |  |  |  |
Amount of Gain Recognized in OCI on Derivatives (Effective Portion) | 384 | (338) | 1,415 | (3)
Amount of Loss (Gain) Reclassified from Accumulated OCI into Income (Effective Portion) | $ (94) | $ 174 | $ (69) | $ 400

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- Definition The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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