Business Segment Information - Intra-Segment and Inter-Segment Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 73,543	$ 84,987	$ 93,870	$ 92,651	$ 99,982	$ 101,596	$ 112,258	$ 103,175	$ 345,051	$ 417,011	$ 367,422
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales									127,279	153,344	158,371
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales									149,514	203,376	142,150
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales									69,159	61,783	67,610
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales									(901)	(1,492)	(709)
Intra - Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(15,238)	(9,476)	(13,897)
Intra - Segment Sales [Member] | Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales									(3,235)	(4,256)	(6,744)
Intra - Segment Sales [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales									(8,834)	(3,506)	(4,876)
Intra - Segment Sales [Member] | Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales									(3,169)	(1,714)	(2,277)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									363,464	432,566	384,992
Operating Segments [Member] | Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales									131,356	160,959	167,247
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales									158,456	207,280	147,661
Operating Segments [Member] | Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales									73,652	64,327	70,084
Inter-segment Elimination [Member] | Environmental Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(601)	(715)	(832)
Inter-segment Elimination [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(1,619)	(3,666)	(1,937)
Inter-segment Elimination [Member] | Fluid Handling Filtration Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(55)	(206)	(195)
Inter-segment Elimination [Member] | Corporate And Other Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(901)	(1,492)	(709)
Inter-segment Elimination [Member] | Environmental Segment [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(787)	(3,153)	(1,937)
Inter-segment Elimination [Member] | Environmental Segment [Member] | Fluid Handling Filtration Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(55)	(206)	(195)
Inter-segment Elimination [Member] | Energy Segment [Member] | Environmental Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(108)	(398)	(635)
Inter-segment Elimination [Member] | Fluid Handling and Filtration Segment [Member] | Environmental Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(493)	(317)	(197)
Inter-segment Elimination [Member] | Fluid Handling and Filtration Segment [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									(832)	(513)
Inter-segment Elimination [Member] | Corporate and Other [Member] | Corporate And Other Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales									$ (901)	$ (1,492)	$ (709)