SUMMARIZED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
SUMMARIZED QUARTERLY FINANCIAL DATA (UNAUDITED) [Abstract]
Revenue	$ 366,426		$ 355,144		$ 346,274		$ 349,752		$ 351,488		$ 367,633		$ 347,996		$ 335,120		$ 1,417,596	$ 1,402,237	$ 1,344,195
Gross profit	236,512	[1]	232,506	[2]	225,587	[3]	229,589	[4]	224,805	[5]	246,200	[6]	226,056	[7]	216,757	[8]	924,194	913,818	839,413
Net income	39,831	[1]	36,735	[2]	35,473	[3]	32,556	[4]	34,826	[5]	50,800	[6]	33,614	[7]	33,384	[8]	144,595	152,624	99,365
Basic (in dollars per share)	$ 0.78	[1]	$ 0.72	[2]	$ 0.69	[3]	$ 0.63	[4]	$ 0.68	[5]	$ 0.99	[6]	$ 0.65	[7]	$ 0.65	[8]	$ 2.82	$ 2.97	$ 1.94
Diluted (in dollars per share)	$ 0.78	[1]	$ 0.71	[2]	$ 0.68	[3]	$ 0.63	[4]	$ 0.68	[5]	$ 0.98	[6]	$ 0.65	[7]	$ 0.65	[8]	$ 2.80	$ 2.96	$ 1.94
Cash dividends per share (in dollars per share)	$ 0.25		$ 0.25		$ 0.25		$ 0.25		$ 0.25		$ 0.25		$ 0.25		$ 0.25		$ 1.00	$ 1.00	$ 1.00
Net pre-tax restructuring charges	3,045		4,598		4,604		1,474		7,754				2,093				13,721	10,327	11,986
Asset impairment charges	1,196																1,196	0	24,900
Tax expense (credit) for discrete items											$ (1,482)		$ (1,384)		$ 3,662

[1] 2011 fourth quarter results included net pre-tax restructuring charges of $3,045 related to our cost reduction initiatives and an asset impairment charge of $1,196 related to a vacant facility which is held for sale.

[2] 2011 third quarter results included net pre-tax restructuring charges of $4,598 related to our cost reduction initiatives.

[3] 2011 second quarter results include net pre-tax restructuring charges of $4,604 related to our cost reduction initiatives.

[4] 2011 first quarter results include net pre-tax restructuring charges of $1,474 related to our cost reduction initiatives.

[5] 2010 fourth quarter results include net pre-tax restructuring charges of $7,754 related to our cost reduction initiatives.

[6] 2010 third quarter results include a $1,482 reduction in income tax expense for discrete items, primarily adjustments to accruals for uncertain tax positions.

[7] 2010 second quarter results include net pre-tax restructuring charges of $2,093 related to our cost reduction initiatives. Results also include a $1,384 reduction in income tax expense for discrete items, primarily reductions in accruals for uncertain tax positions.

[8] 2010 first quarter results include tax expense of $3,662 for discrete items, primarily the impact of recent health care legislation on deferred income taxes.