Business Segment Information - Net Sales and Income from Operation by Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net sales	$ 112,258	$ 86,961	$ 215,433	$ 167,946
Income from operations	8,561	4,488	14,368	7,467
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales	44,211	41,798	83,333	83,514
Income from operations	6,119	5,140	10,865	9,158
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	52,867	27,303	100,799	51,652
Income from operations	6,367	215	11,563	635
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	15,413	17,745	32,008	32,939
Income from operations	3,200	4,431	6,398	7,387
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales	(233)	115	(707)	(159)
Income from operations	(6,618)	(5,074)	(13,537)	(8,891)
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Income from operations	$ (507)	$ (224)	$ (921)	$ (822)