Acquisitions - Additional Information (Detail)	0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended		0 Months Ended	12 Months Ended		12 Months Ended			0 Months Ended			12 Months Ended	0 Months Ended		12 Months Ended
	Dec. 15, 2014 Zhongli [Member] USD ($)	Dec. 31, 2014 Zhongli [Member] USD ($)	Dec. 15, 2014 Zhongli [Member] USD ($)	Nov. 30, 2014 Emtrol [Member] USD ($)	Dec. 31, 2014 Emtrol [Member] USD ($)	Nov. 30, 2014 Emtrol [Member] Thirty Trading Days [Member] USD ($)	Sep. 26, 2014 SAT Technology, Inc. ("SAT") [Member] USD ($)	Dec. 31, 2014 SAT Technology, Inc. ("SAT") [Member] USD ($)	Sep. 26, 2014 SAT Technology, Inc. ("SAT") [Member] USD ($)	Aug. 13, 2014 HEE [Member] USD ($)	Dec. 31, 2014 HEE [Member] USD ($)	Aug. 13, 2014 HEE [Member] Thirty Trading Days [Member] USD ($)	Dec. 31, 2014 Aarding Thermal Acoustics B.V. ("Aarding") [Member] USD ($)	Dec. 31, 2013 Aarding Thermal Acoustics B.V. ("Aarding") [Member] USD ($)	Dec. 31, 2014 Aarding Thermal Acoustics B.V. ("Aarding") [Member] EUR (€)	Nov. 30, 2014 Maximum [Member] Emtrol [Member]	Nov. 30, 2014 Minimum [Member] Emtrol [Member]	Aug. 27, 2013 Met-Pro [Member] USD ($)	Dec. 31, 2014 Met-Pro [Member] USD ($)	Aug. 27, 2013 Met-Pro [Member] Maximum [Member]	Aug. 27, 2013 Met-Pro [Member] Minimum [Member]	Dec. 31, 2014 Met-Pro [Member] Minimum [Member]
Business Acquisition [Line Items]
Equity interests acquired			100.00%	100.00%					100.00%
Cash paid on acquisition	$ 7,000,000			$ 31,900,000			$ 1,400,000			$ 7,000,000			$ 24,400,000
Earn out payment upon attainment of specified financial targets through December 31, 2015			0							2,000,000	0		6,700,000		5,500,000
Earn out expenses	17,100,000						1,000,000	0					1,500,000	1,300,000
First year estimated earn-out payable			6,100,000					300,000			700,000
Remainder of estimated earn-out payable			11,000,000					700,000			1,300,000
Revenue contributed		100,000			9,800,000			1,000,000			2,300,000
Net income contributed		0			1,300,000			0			100,000
Company's common stock				453,858						34,626			763,673
Fair value of common stock issued				5,800,000		6,000,000				500,000		500,000	6,800,000
Trading day period				30 days						30 days									15 days
Restrictions on sale or transfer for periods range										6 months						2 years	1 year
Cash held back									200,000
Business combination contingent consideration paid													4,900,000		4,000,000
Prepaid compensation recognized in Prepaid expenses and other current assets													1,000,000	1,100,000
Prepaid compensation recognized in Deferred Charges and other assets													2,100,000	3,500,000
Business combination compensation expenses													1,100,000	900,000
Earn out expenses included in accounts payable and accrued expenses													1,100,000	1,300,000
Cash consideration per share																		$ 13.75
Stock consideration per share																			$ 13.75
Exchange ratio																		1.0843		1.3520	1.0000	1.0000
Percentage of common stock converted into cash																			51.60%
Value of shares transferred for cash																			104,400,000
Trading price																			$ 12.6814
Shares of common stock in aggregate stock consideration																			7,726,235
Percentage of cash consideration																			77.56%
Percentage of stock consideration																			22.44%
Value of stock recorded																			98,000,000
Consideration for cancelling of options and restricted stock units																			4,900,000
Proceeds from properties sold																			$ 6,700,000