Segment Information Applicable to Reportable Operating Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net sales:
Net sales	$ 556,247	$ 561,294	$ 542,569	$ 498,763	$ 553,162	$ 575,646	$ 512,561	$ 461,926	$ 2,158,873	$ 2,103,295	$ 1,974,198
Operating income (loss):
Operating income (loss)	14,638	16,300	14,668	9,026	11,783	15,882	12,417	7,529	54,632	47,611	38,667
Interest expense	(33)	(69)	(64)		(148)	(93)	(87)	(41)	(166)	(369)	(490)
Other, net	18	6	(29)	46	60	32	32	65	41	189	213
Income before taxes	14,623	16,237	14,575	9,072	11,695	15,821	12,362	7,553	54,507	47,431	38,390
Depreciation and amortization:
Depreciation and amortization									6,895	5,951	5,430
Special charges				1,135					1,135
Total assets:
Total assets	468,323				468,019				468,323	468,019
Small and Medium Sized Businesses segment
Net sales:
Net sales									902,642	922,439	908,141
Operating income (loss):
Operating income (loss)									31,730	26,725	20,422
Depreciation and amortization:
Depreciation and amortization									9	26	52
Total assets:
Total assets	146,633				131,036				146,633	131,036
Large Account Segment
Net sales:
Net sales									773,352	711,177	603,177
Operating income (loss):
Operating income (loss)									32,764	28,644	26,356
Depreciation and amortization:
Depreciation and amortization									2,156	1,377	443
Total assets:
Total assets	221,171				197,715				221,171	197,715
Public Sector
Net sales:
Net sales									482,879	469,679	462,880
Operating income (loss):
Operating income (loss)									8,316	4,886	4,150
Depreciation and amortization:
Depreciation and amortization									165	170	109
Total assets:
Total assets	63,210				74,788				63,210	74,788
Headquarters and Other
Operating income (loss):
Operating income (loss)									(18,178)	(12,644)	(12,261)
Depreciation and amortization:
Depreciation and amortization									4,565	4,378	4,826
Special charges									1,135
Total assets:
Total assets	$ 37,309				$ 64,480				$ 37,309	$ 64,480