Business Segment Information - Net Sales and Income from Operation by Business Segment (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
Income from operations	9,255	8,561	10,605	14,368
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	37,879	44,211	73,808	83,333
Income from operations	4,777	6,119	9,886	10,865
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	37,416	52,867	78,499	100,799
Income from operations	7,528	6,367	9,141	11,563
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	18,348	15,413	34,164	32,008
Income from operations	4,148	3,200	7,457	6,398
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales	227	(233)	50	(707)
Income from operations	(6,769)	(6,618)	(14,780)	(13,537)
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Income from operations	$ (429)	$ (507)	$ (1,099)	$ (921)