Revolving Credit Facilities (Details) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	Feb. 22, 2016 USD ($)	Mar. 31, 2018	Sep. 30, 2018 USD ($)	Dec. 31, 2018	Sep. 30, 2018 USD ($)	Jul. 01, 2018	Dec. 31, 2017 USD ($)	Aug. 10, 2010 USD ($)
Line of Credit Facility [Line Items]
Maturity date		Sep. 25, 2019
Line of Credit, Current			$ 12,979		$ 12,979		$ 0
Required interest coverage ratio			5.00		5.00
Letters of credit to be drawn			$ 500		$ 500
Long-term Line of Credit, Noncurrent			$ 138,447		138,447		$ 128,398
Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate			5000.00%
Eurodollar [Member] | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate			15000.00%
Base Rate [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	110.00%
International
Line of Credit Facility [Line Items]
Revolving commitment amount	$ 5,000
Unused capacity			$ 4,500		4,500
North America
Line of Credit Facility [Line Items]
Unused capacity			$ 3,600		$ 3,600
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving commitment amount								$ 175,000
Credit Agreement Due 2020 [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving commitment amount								160,000
August 2010 Credit Facility Agreement
Line of Credit Facility [Line Items]
Required ratio of indebtedness to net capital			3.0		3.0
Maximum leverage ratio					4.25
August 2010 Credit Facility Agreement | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Increase in aggregate commitment amount								$ 50,000
August 2018 Credit Facility Agreement
Line of Credit Facility [Line Items]
Required ratio of indebtedness to net capital						3.0
Maximum leverage ratio				3.50
August 2018 Credit Facility Agreement | Maximum
Line of Credit Facility [Line Items]
Required ratio of indebtedness to net capital			3.00		3.00