SUMMARIZED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Data [Abstract]
Total revenue	$ 417,758	$ 398,080	$ 381,433	$ 387,553	$ 387,584	$ 378,338	$ 371,014	$ 377,981	$ 1,584,824	$ 1,514,917	$ 1,417,596
Gross profit	265,709	255,857	247,886	254,256	249,980	246,648	243,420	250,494	1,023,708	990,542	924,194
Net income	45,722	46,903	48,152	45,875	42,648	41,503	42,262	44,079	186,652	170,492	144,595
Earnings per share:
Earnings per share - basic	$ 0.90	$ 0.93	$ 0.95	$ 0.90	$ 0.83	$ 0.81	$ 0.83	$ 0.86	$ 3.68	$ 3.33	$ 2.82
Earnings per share - diluted	$ 0.90	$ 0.92	$ 0.94	$ 0.89	$ 0.83	$ 0.81	$ 0.82	$ 0.86	$ 3.65	$ 3.32	$ 2.80
Cash dividends per share	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 1.00	$ 1.00	$ 1.00
Items affecting comparability of results
Net pre-tax restructuring charges	5,327	3,079	1,051	1,449	4,002	2,934	1,921	1,877	10,906	10,734	13,721
Reduction in income tax expense for discrete items					1,731	1,097
Loss on early debt extinguishment					5,258				0	5,258	6,995
Impairment charge	$ 5,000								$ 5,000	$ 0	$ 1,196