Risk Management and Derivatives (Classification on the Consolidated Statements of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Expense \| Interest rate cap \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	$ 495	$ 0	$ 0
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	339	(185)	(626)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Ineffective Portion)	132
Interest Expense \| Interest rate swaps \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)		(175)	(537)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)		(32)	170
Earnings from equity method investments \| Interest rate cap \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	(16)	(4)	(13)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	(16)	(3)	(1)
Earnings from equity method investments \| Interest rate swaps \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	368	94	(528)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	(285)	(378)	(464)
Earnings from equity method investments \| Foreign exchange contracts \| Designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain (Loss) Recognized in Accumulated Other Comprehensive Income (Effective Portion)	(352)	(167)	(124)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Earnings (Effective Portion)	0	0	0
Other Expense \| Interest rate cap \| Not designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain or (Loss) Recognized in Income	6	(1,080)	(3,671)
Other Expense \| Foreign exchange contracts \| Not designated as hedge
Derivative financial instruments on consolidated statements of operations
Amount of Gain or (Loss) Recognized in Income	$ (970)	$ 1,115	$ 2,403

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=84234895&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=84234895&loc=SL5624171-113959

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+ 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 (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Section 50
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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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