Industry Segment and Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 112,329	$ 113,587	$ 91,119	$ 108,508	$ 107,556	$ 108,646	$ 103,542	$ 104,881	$ 425,544	$ 424,625	$ 433,732
Long-lived assets	82,705				85,761				82,705	85,761
Total assets	468,380				421,893				468,380	421,893
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									376,426	369,163	374,650
Long-lived assets	48,805				51,539				48,805	51,539
Total assets	365,748				326,248				365,748	326,248
Asia
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									6,437	9,111	9,081
Canada
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									10,406	13,568	11,893
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									18,255	15,784	20,147
Long-lived assets	15,142				14,768				15,142	14,768
Total assets	80,337				72,296				80,337	72,296
Mexico
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									4,886	5,791	3,603
Long-lived assets	18,758				19,454				18,758	19,454
Total assets	$ 22,295				$ 23,349				22,295	23,349
Middle East
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									6,114	7,868	11,318
Other
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues									$ 3,020	$ 3,340	$ 3,040