Business Segment Information - Intra-Segment and Inter-Segment Revenues (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Intra-Segment Sales									$ (14,898)	$ (9,194)	$ (5,458)
Net Sales to Outside Customers	68,727	49,796	44,433	34,361	76,106	63,300	66,641	57,170	263,217	197,317	135,052
Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Intra-Segment Sales									(7,089)	(6,552)	(5,451)
Net Sales to Outside Customers									127,707	101,150	88,582
Energy Segment [Member]
Segment Reporting Information [Line Items]
Intra-Segment Sales									(5,964)	(1,921)	(7)
Net Sales to Outside Customers									70,285	69,355	40,194
Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Intra-Segment Sales									(1,845)	(721)
Net Sales to Outside Customers									65,638	25,199	6,191
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Sales to Outside Customers									(413)	1,613	85
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Sales									280,404	208,053	142,256
Operating Segments [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Total Sales									136,544	108,939	95,358
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Total Sales									76,302	71,455	40,650
Operating Segments [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Total Sales									67,558	26,181	6,229
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Total Sales										1,478	19
Inter-segment Elimination [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Air Pollution Control									(128)	(440)	(487)
Inter-Segment Sales by APC to Energy Segment									(1,403)	(831)	(346)
Inter-Segment Sales to Fluid Handling Filtration									(345)	(406)	(979)
Inter-Segment Sales to Corporate and Other									(413)	135	66
Inter-segment Elimination [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales by APC to Energy Segment									(1,403)	(831)	(346)
Inter-Segment Sales to Fluid Handling Filtration									(345)	(406)	(979)
Inter-segment Elimination [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Air Pollution Control									(53)	(179)	(449)
Inter-segment Elimination [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Air Pollution Control									(75)	(261)	(38)
Inter-segment Elimination [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Inter-Segment Sales to Corporate and Other									$ (413)	$ 135	$ 66