SEGMENT AND GEOGRAPHICAL REPORTING, Business Segmented Financial Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Sales	$ 1,097,110	$ 807,005	$ 656,202
Operating income for reportable segments	133,518	89,866	68,004
Identifiable assets at year end	547,768	394,104	311,286
Capital expenditures	5,090	1,641	1,184
Depreciation	6,215	2,692	3,183
Amortization	10,886	6,572	5,824
Interest expense	5,560	3,518	5,208
Service Centers [Member]
Segment Reporting Information [Line Items]
Sales	779,038	560,233	452,719
Operating income for reportable segments	88,924	64,491	50,549
Identifiable assets at year end	440,271	294,410	240,068
Capital expenditures	4,829	1,258	1,075
Depreciation	5,734	2,090	2,426
Amortization	8,795	4,725	4,055
Interest expense	3,701	2,073	4,115
IPS [Member]
Segment Reporting Information [Line Items]
Sales	161,834	102,305	77,024
Operating income for reportable segments	32,099	16,920	10,335
Identifiable assets at year end	56,982	43,636	25,405
Capital expenditures	261	310	17
Depreciation	306	326	368
Amortization	663	675	604
Interest expense	1,243	986	700
SCS [Member]
Segment Reporting Information [Line Items]
Sales	156,238	144,467	126,459
Operating income for reportable segments	12,495	8,455	7,120
Identifiable assets at year end	50,515	56,058	45,813
Capital expenditures	0	73	92
Depreciation	175	276	389
Amortization	1,428	1,172	1,165
Interest expense	$ 616	$ 459	$ 393