Business Segment Information - Net Sales and Operating Income (Loss) by Business Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Net sales	$ 66,641	$ 44,433	$ 123,811	$ 78,794
Net operating income	7,188	3,307	12,680	6,645
Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Net sales	32,939	24,069	59,687	44,589
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net sales	16,835	18,996	32,116	31,019
Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net sales	16,650	1,245	32,145	2,890
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net sales	217	123	(137)	296
Operating Segments [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Net operating income	4,876	3,839	8,742	7,150
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Net operating income	1,596	3,135	3,983	5,413
Operating Segments [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net operating income	3,069	259	5,740	441
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net operating income	(2,221)	(3,689)	(4,956)	(6,152)
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Net operating income	$ (132)	$ (237)	$ (829)	$ (207)