BUSINESS ACQUISITIONS (Details)	12 Months Ended			12 Months Ended			0 Months Ended				0 Months Ended					12 Months Ended		12 Months Ended
	Dec. 31, 2012 USD ($)	Jul. 11, 2012 USD ($)	May 31, 2012 USD ($)	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2012 Maximum [Member]	Oct. 10, 2011 Kenneth Crosby [Member] USD ($)	Dec. 30, 2011 C.W.Rod Tool Company [Member] USD ($)	Jan. 31, 2012 Mid-Continent Safety [Member] USD ($)	Feb. 29, 2012 Pump & Power Equipment, Inc. [Member] USD ($)	Apr. 02, 2012 Aledco, Inc. [Member] USD ($)	May 01, 2012 Industrial Paramedic Services [Member] USD ($)	Dec. 31, 2012 Industrial Paramedic Services [Member] Promissory Notes [Member] USD ($)	Dec. 31, 2012 HSE Integrated Ltd. [Member] USD ($)	Jul. 11, 2012 HSE Integrated Ltd. [Member] USD ($)	Jul. 11, 2012 HSE Integrated Ltd. [Member] CAD	Dec. 31, 2011 Indian Fire & Safety [Member] USD ($)	Oct. 01, 2012 Jerzy Supply, Inc. [Member] USD ($)	Dec. 31, 2012 Units acquired in 2011 and 2012 [Member] USD ($)	Dec. 31, 2011 Units acquired in 2011 and 2012 [Member] USD ($)	Dec. 31, 2011 Units acquired in 2011 and 2010 [Member] USD ($)	Dec. 31, 2010 Units acquired in 2011 and 2010 [Member] USD ($)
Business Acquisition [Line Items]
Contingent payments																$ 1,000,000
Purchase price			2,700,000			15,600,000	41,700,000	3,700,000	1,900,000	8,100,000	25,300,000			85,000,000			5,300,000
Borrowings under existing credit facility						15,600,000	41,700,000	3,700,000	1,900,000	8,100,000	20,600,000
Goodwill on acquisition			300,000			5,800,000	10,000,000	1,200,000	700,000	3,400,000	12,100,000			25,800,000
Purchase price, common stock							1,100,000
Number of shares issued on acquisition (in shares)							35,714				19,685
Purchase price, cash paid							41,700,000
Cash paid in form of checks							36,700,000
Number of operating locations											3
Borrowings under notes												2,500,000
Stated interest rate (in hundredths)											5.00%
Share price (in dollars per share)															1.8
Liabilities assumed on acquisiton		4,000,000
Transaction cost													3,000,000
New credit facility, maximum borrowing capacity		325,000,000
Discount rate for valuation of acquired intangibles (in hundredths)				17.00%	28.20%
Sales from business acquisitions	204,800,000
Earnings from business acquisitions	5,800,000
Pro Forma Information [Abstract]
Net sales																		1,177,091,000	1,062,540,000	903,240,000	778,267,000
Net income																		54,033,000	41,359,000	35,511,000	22,898,000
Per share data [Abstract]
Basic earnings (in dollars per share)																		$ 3.75	$ 2.88	$ 2.48	$ 1.65
Diluted earnings (in dollars per share)																		$ 3.55	$ 2.72	$ 2.35	$ 1.56
Purchase price allocation [Abstract]
Cash	12,377,000
Accounts Receivable, net	50,645,000
Inventory, net	17,805,000
Property and equipment	36,303,000
Goodwill and intangibles	108,842,000
Other assets	2,839,000
Assets acquired	228,811,000
Current liabilities assumed	(32,166,000)
Non current liabilities assumed	(15,296,000)
Net assets acquired	$ 181,349,000