Derivative Financial Instruments - Schedule of Derivative Financial Instruments (Details) - Dec. 31, 2017	USD ($) derivative $ / £	GBP (£) derivative $ / £
Interest-rate swap contracts \| Cash flow hedge
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional	$ 44,000,000
Pay Rate/Receive Rate (as a percent)	3.82%	3.82%
Fair value of interest rate hedge, liabilities	$ (2,483,000)
Cross Currency Interest Rate Contract \| Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional \| £		£ 105,000,000
Fair value of interest rate hedge, liabilities	$ (10,968,000)
Foreign currency translation rate (as a percent) \| $ / £	1.251	1.251
Cross Currency Interest Rate Contract \| Long \| Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional \| £		£ 105,000,000
Pay Rate/Receive Rate (as a percent)	2.584%	2.584%
Cross Currency Interest Rate Contract \| Short \| Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional	$ 131,000,000
Pay Rate/Receive Rate (as a percent)	3.75%	3.75%
Interest rate swap, entered in July 2005, maturity in July 2020 \| Cash flow hedge
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of interest-rate swap contracts \| derivative	3	3

Nominal or face amount used to calculate payments on the derivative asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

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Fixed interest rate related to the interest rate derivative.

+ References

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Foreign exchange rate used to translate amounts denominated in functional currency to reporting currency.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6897108&loc=SL6897125-166521

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Fair value as of the balance sheet date of all interest rate derivative liabilities designated as cash flow hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

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Number of interest rate derivative instruments held by the entity at the reporting date.

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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 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

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