Industry Segment and Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 107,556	$ 108,646	$ 103,542	$ 104,881	$ 104,413	$ 110,630	$ 113,648	$ 105,041	$ 424,625	$ 433,732	$ 402,440
Long-lived assets	85,761				90,321				85,761	90,321
Total assets	421,893				392,691				421,893	392,691
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									369,163	374,650	355,768
Long-lived assets	51,539				54,904				51,539	54,904
Total assets	326,248				293,943				326,248	293,943
Asia
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									9,111	9,081	9,133
Canada
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									13,568	11,893	10,407
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									15,784	20,147	15,718
Long-lived assets	14,768				15,247				14,768	15,247
Total assets	72,296				74,707				72,296	74,707
Mexico
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									5,791	3,603	3,601
Long-lived assets	19,454				20,170				19,454	20,170
Total assets	$ 23,349				$ 24,041				23,349	24,041
Middle East
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									7,868	11,318	4,904
Other
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									$ 3,340	$ 3,040	$ 2,909