Business Segment Information - Intra-Segment and Inter-Segment Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 103,175	$ 80,985
Intra - Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(2,648)	(2,954)
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	39,122	41,716
Environmental Segment [Member] | Intra - Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(1,754)	(1,807)
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	47,932	24,349
Energy Segment [Member] | Intra - Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(491)	(695)
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	16,595	15,194
Fluid Handling and Filtration Segment [Member] | Intra - Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(403)	(452)
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales	(474)	(274)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	107,646	84,372
Operating Segments [Member] | Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	42,053	43,557
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	48,581	25,081
Operating Segments [Member] | Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	17,012	15,734
Inter-segment Elimination [Member] | Air Pollution Control Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(172)	(125)
Inter-segment Elimination [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(1,040)	(34)
Inter-segment Elimination [Member] | Fluid Handling Filtration Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(137)
Inter-segment Elimination [Member] | Corporate And Other Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(474)	(274)
Inter-segment Elimination [Member] | Environmental Segment [Member] | Energy Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(1,040)	(34)
Inter-segment Elimination [Member] | Environmental Segment [Member] | Fluid Handling Filtration Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(137)
Inter-segment Elimination [Member] | Energy Segment [Member] | Air Pollution Control Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(158)	(37)
Inter-segment Elimination [Member] | Fluid Handling and Filtration Segment [Member] | Air Pollution Control Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	(14)	(88)
Inter-segment Elimination [Member] | Corporate and Other [Member] | Corporate And Other Inter-Segment Sales [Member]
Segment Reporting Information [Line Items]
Net sales	$ (474)	$ (274)