Business Segment Information - Intra-Segment and Inter-Segment Revenues (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]
Intra- Segment Sales	$ (4,147)	$ (3,220)	$ (6,430)	$ (4,405)
Net Sales to Outside Customers	66,641	44,433	123,811	78,794
Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Intra- Segment Sales	(2,461)	(2,549)	(3,490)	(3,705)
Net Sales to Outside Customers	32,939	24,069	59,687	44,589
Energy Segment [Member]
Segment Reporting Information [Line Items]
Intra- Segment Sales	(1,284)	(671)	(2,193)	(700)
Net Sales to Outside Customers	16,835	18,996	32,116	31,019
Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Intra- Segment Sales	(402)		(747)
Net Sales to Outside Customers	16,650	1,245	32,145	2,890
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Sales to Outside Customers	217	123	(137)	296
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Sales	70,791	47,568	130,905	83,353
Operating Segments [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	35,576	26,635	63,660	48,721
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	18,120	19,667	34,310	31,721
Operating Segments [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	17,095	1,266	32,935	2,911
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Air Pollution Control	(44)	(21)	(44)	(23)
Inter-Segment Sales by APC to Energy Segment	(15)	(12)	(322)	(28)
Inter-Segment Sales to Fluid Handling Filtration	(161)	(5)	(161)	(399)
Inter-Segment Sales to Corporate and Other	217	123	(137)	296
Inter-segment Elimination [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales by APC to Energy Segment	(15)	(12)	(322)	(28)
Inter-Segment Sales to Fluid Handling Filtration	(161)	(5)	(161)	(399)
Inter-segment Elimination [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Air Pollution Control	(1)		(1)	(2)
Inter-segment Elimination [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Air Pollution Control	(43)	(21)	(43)	(21)
Inter-segment Elimination [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Corporate and Other	$ 217	$ 123	$ (137)	$ 296