Summary of Operations and Significant Accounting Policies - Component of Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Unrealized foreign currency losses	$ (42,010)	$ (75,075)
Unrealized gain on interest rate swap, net of tax	2,524	1,506
Unrealized loss on defined benefit plan	$ (43,994)	$ (39,097)

Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant