Industry Segment and Geographic Areas (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting [Abstract]
Number of segments | segment									1
Revenues from External Customers and Long-Lived Assets
Revenues	$ 96,650	$ 100,008	$ 104,176	$ 101,606	$ 93,098	$ 96,273	$ 103,820	$ 100,570	$ 402,440	$ 393,761	$ 377,698
Long-lived assets	93,601				90,194				93,601	90,194
Total assets	391,727				349,699				391,727	349,699
United States
Revenues from External Customers and Long-Lived Assets
Revenues									355,768	347,853	322,535
Long-lived assets	56,980				53,454				56,980	53,454
Total assets	300,688				287,081				300,688	287,081
Asia
Revenues from External Customers and Long-Lived Assets
Revenues									9,133	6,539	8,299
Canada
Revenues from External Customers and Long-Lived Assets
Revenues									10,407	12,587	9,095
Europe
Revenues from External Customers and Long-Lived Assets
Revenues									15,718	15,299	17,036
Long-lived assets	15,806				15,694				15,806	15,694
Total assets	66,862				38,579				66,862	38,579
Mexico
Revenues from External Customers and Long-Lived Assets
Revenues									3,601	3,460	8,889
Long-lived assets	20,815				21,046				20,815	21,046
Total assets	$ 24,177				$ 24,039				24,177	24,039
Middle East
Revenues from External Customers and Long-Lived Assets
Revenues									4,904	5,520	9,672
Other
Revenues from External Customers and Long-Lived Assets
Revenues									$ 2,909	$ 2,503	$ 2,172