SEGMENT REPORTING (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Adjustment for [Abstract]
Amortization of intangibles			$ 13,874	$ 9,221
Operating income	31,804	26,898	82,364	72,867
Interest expense, net	3,295	1,614	9,868	4,930
Other expense (income), net	10	(38)	1	(16)
Income before income taxes	28,499	25,322	72,495	67,953
Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales	387,053	329,719	1,117,160	927,758
Operating income for reportable segments	48,144	39,818	130,108	109,793
Adjustment for [Abstract]
Operating income	31,804	26,898	82,364	72,867
Operating Segments [Member] | Service Centers [Member]
Segment Reporting Information [Line Items]
Sales	255,041	232,529	735,104	660,552
Operating income for reportable segments	29,444	27,557	79,356	75,976
Operating Segments [Member] | IPS [Member]
Segment Reporting Information [Line Items]
Sales	88,614	61,094	259,070	155,572
Operating income for reportable segments	14,979	9,059	40,328	24,267
Operating Segments [Member] | SCS [Member]
Segment Reporting Information [Line Items]
Sales	43,398	36,096	122,986	111,634
Operating income for reportable segments	3,721	3,202	10,424	9,550
Segment Reconciling Items [Member]
Adjustment for [Abstract]
Amortization of intangibles	4,651	3,434	13,874	9,221
Corporate and other expense, net	$ 11,689	$ 9,486	$ 33,870	$ 27,705