QUARTERLY RESULTS (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
QUARTERLY RESULTS (UNAUDITED)
Sales	$ 223,148	$ 239,543	$ 238,650	$ 220,858	$ 239,784	$ 202,149	$ 192,275	$ 175,259	$ 922,200	$ 809,467	$ 780,033
Gross profit	70,650	78,851	76,493	68,401	77,196	67,452	63,040	56,661	294,397	264,349	269,443
Net income	$ 17,443	$ 18,389	$ 12,975	$ 9,202	$ 10,793	$ 6,340	$ 8,676	$ 2,215	$ 58,011	$ 28,024	$ 27,353
Earnings per share - basic	$ 0.38	$ 0.40	$ 0.28	$ 0.20	$ 0.24	$ 0.14	$ 0.19	$ 0.05	$ 1.25	$ 0.61	$ 0.60
Earnings per share - diluted	$ 0.37	$ 0.39	$ 0.28	$ 0.20	$ 0.23	$ 0.14	$ 0.19	$ 0.05	$ 1.24	$ 0.61	$ 0.60