SEGMENT AND GEOGRAPHICAL REPORTING, Business Segmented Financial Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Sales	$ 1,241,510	$ 1,097,110	$ 807,005
Operating income for reportable segments	153,398	133,518	89,866
Identifiable assets at year end	615,034	547,768	394,104
Capital expenditures	6,884	5,090	1,641
Depreciation	8,582	6,215	2,692
Amortization	11,830	10,886	6,572
Interest expense	6,282	5,560	3,518
Service Centers [Member]
Segment Reporting Information [Line Items]
Sales	884,821	779,038	560,233
Operating income for reportable segments	107,142	88,924	64,491
Identifiable assets at year end	500,978	440,271	294,410
Capital expenditures	6,321	4,829	1,258
Depreciation	7,770	5,734	2,090
Amortization	8,574	8,795	4,725
Interest expense	3,762	3,701	2,073
IPS [Member]
Segment Reporting Information [Line Items]
Sales	209,175	161,834	102,305
Operating income for reportable segments	33,766	32,099	16,920
Identifiable assets at year end	66,007	56,982	43,636
Capital expenditures	357	261	310
Depreciation	446	306	326
Amortization	1,043	663	675
Interest expense	1,636	1,243	986
SCS [Member]
Segment Reporting Information [Line Items]
Sales	147,514	156,238	144,467
Operating income for reportable segments	12,490	12,495	8,455
Identifiable assets at year end	48,049	50,515	56,058
Capital expenditures	206	0	73
Depreciation	366	175	276
Amortization	2,213	1,428	1,172
Interest expense	$ 884	$ 616	$ 459