Business Segment Information - Property and Equipment Additions, Depreciation and Amortization and Identifiable Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Property and equipment additions	$ 119	$ 415
Depreciation and amortization	3,452	2,770
Identifiable Assets	417,428		414,365
Air Pollution Control Segment [Member]
Segment Reporting Information [Line Items]
Property and equipment additions	64	136
Depreciation and amortization	1,153	395
Identifiable Assets	133,504		133,899
Energy Segment [Member]
Segment Reporting Information [Line Items]
Property and equipment additions	40	34
Depreciation and amortization	671	655
Identifiable Assets	94,152		91,850
Fluid Handling Filtration Segment [Member]
Segment Reporting Information [Line Items]
Property and equipment additions	5	214
Depreciation and amortization	1,596	1,688
Identifiable Assets	172,692		172,779
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Property and equipment additions	10	31
Depreciation and amortization	32	32
Identifiable Assets	$ 17,080		$ 15,837