Business Segment Information - Net Sales and Income from Operation by Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 73,543	$ 84,987	$ 93,870	$ 92,651	$ 99,982	$ 101,596	$ 112,258	$ 103,175	$ 345,051	$ 417,011	$ 367,422
Income (loss) from Operations									8,024	(25,562)	4,949
Environmental Segment [Member]
Segment Reporting Information [Line Items]
Net sales									127,279	153,344	158,371
Income (loss) from Operations									13,703	15,652	17,021
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales									149,514	203,376	142,150
Income (loss) from Operations									8,987	23,575	3,488
Fluid Handling and Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales									69,159	61,783	67,610
Income (loss) from Operations									14,734	(36,209)	11,741
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales									(901)	(1,492)	(709)
Income (loss) from Operations									(26,649)	(26,981)	(26,592)
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Income (loss) from Operations									$ (2,751)	$ (1,599)	$ (709)