Business Segments - Assets by Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Net	$ 36,714	$ 37,212	$ 36,030	$ 34,000	$ 32,656	$ 32,279	$ 33,089	$ 33,208
Total assets	649,638	$ 660,532	$ 616,620	$ 600,086	593,987	$ 613,393	$ 597,148	$ 599,321
United States
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Net	21,800				21,200
North America
Segment Reporting Information [Line Items]
Total assets	401,415				370,403
International
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Net	14,900				11,400
Total assets	228,321				203,238
Other Geographical Region
Segment Reporting Information [Line Items]
Total assets	$ 19,902				$ 20,346