Business Segment Information - Intra-Segment and Inter-Segment Revenues (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Net Sales to Outside Customers	$ 80,985	$ 57,170
Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Net Sales to Outside Customers	41,716	26,748
Energy Segment [Member]
Segment Reporting Information [Line Items]
Net Sales to Outside Customers	24,349	15,281
Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Net Sales to Outside Customers	15,194	15,495
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Sales to Outside Customers	(274)	(354)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Sales	84,372	60,114
Operating Segments [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	43,557	28,084
Operating Segments [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	25,081	16,190
Operating Segments [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	15,734	15,840
Intra-segment Sales [Member]
Segment Reporting Information [Line Items]
Total Sales	2,954	2,283
Intra-segment Sales [Member] | Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	1,807	1,029
Intra-segment Sales [Member] | Energy Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	695	909
Intra-segment Sales [Member] | Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Total Sales	452	345
Inter-segment Elimination [Member] | APC [Member]
Segment Reporting Information [Line Items]
Total Sales	125
Inter-segment Elimination [Member] | Energy [Member]
Segment Reporting Information [Line Items]
Total Sales	34	307
Inter-segment Elimination [Member] | Corp and Other [Member]
Segment Reporting Information [Line Items]
Total Sales	(274)	(354)
Inter-segment Elimination [Member] | Air Pollution Control Segment [Member] | Energy [Member]
Segment Reporting Information [Line Items]
Total Sales	34	307
Inter-segment Elimination [Member] | Energy Segment [Member] | APC [Member]
Segment Reporting Information [Line Items]
Total Sales	37
Inter-segment Elimination [Member] | Fluid Handling Filtration Segment [Member] | APC [Member]
Segment Reporting Information [Line Items]
Total Sales	88
Inter-segment Elimination [Member] | Corporate and Other [Member] | Corp and Other [Member]
Segment Reporting Information [Line Items]
Total Sales	$ (274)	$ (354)