Business Segment Information - Net Sales and Income from Operation by Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net sales	$ 101,596	$ 98,230	$ 317,029	$ 266,176
Income (loss) from operations	10,499	(2,194)	24,867	5,273
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	36,606	40,644	119,939	124,158
Income (loss) from operations	5,459	5,225	16,324	14,383
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	50,259	40,014	151,058	91,666
Income (loss) from operations	8,502	(1,082)	20,065	(447)
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	14,866	17,136	46,874	50,075
Income (loss) from operations	3,109	4,011	9,507	11,398
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales	(135)	436	(842)	277
Income (loss) from operations	(6,520)	(11,170)	(20,058)	$ (20,061)
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations	$ (51)	$ 822	$ (971)