Business Segment Information - Intra-Segment and Inter-Segment Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Net sales	$ 93,870	$ 112,258	$ 186,521	$ 215,433
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	37,879	44,211	73,808	83,333
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	37,416	52,867	78,499	100,799
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	18,348	15,413	34,164	32,008
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales	227	(233)	50	(707)
Intra - Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(4,178)	(1,950)	(7,994)	(4,598)
Intra - Segment Sales [Member] | Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	(800)	(844)	(1,690)	(2,598)
Intra - Segment Sales [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	(2,839)	(654)	(5,147)	(1,145)
Intra - Segment Sales [Member] | Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	(539)	(452)	(1,157)	(855)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	98,133	115,307	195,786	222,953
Operating Segments [Member] | Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	38,718	45,522	76,266	87,575
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	40,255	53,740	83,668	102,321
Operating Segments [Member] | Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	19,160	16,045	35,852	33,057
Inter-segment Elimination [Member] | Environmental Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(258)	(399)	(444)	(571)
Inter-segment Elimination [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(15)	(427)	(838)	(1,467)
Inter-segment Elimination [Member] | Fluid Handling Filtration Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(39)	(40)	(39)	(177)
Inter-segment Elimination [Member] | Corporate And Other Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	227	(233)	50	(707)
Inter-segment Elimination [Member] | Environmental Segment [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales		(427)	(729)	(1,467)
Inter-segment Elimination [Member] | Environmental Segment [Member] | Fluid Handling Filtration Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(39)	(40)	(39)	(177)
Inter-segment Elimination [Member] | Energy Segment [Member] | Environmental Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales		(219)	(22)	(377)
Inter-segment Elimination [Member] | Fluid Handling and Filtration Segment [Member] | Environmental Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(258)	(180)	(422)	(194)
Inter-segment Elimination [Member] | Fluid Handling and Filtration Segment [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(15)		(109)
Inter-segment Elimination [Member] | Corporate and Other [Member] | Corporate And Other Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	$ 227	$ (233)	$ 50	$ (707)