QUARTERLY FINANCIAL INFORMATION (Unaudited) (Details) (USD $) In Thousands, except Per Share data, 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, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
QUARTERLY FINANCIAL INFORMATION (Unaudited) [Abstract]
Sales	$ 293,000	$ 289,900	$ 261,900	$ 252,300	$ 218,300	$ 207,900	$ 197,700	$ 183,100	$ 169,700	$ 172,200	$ 167,300	$ 147,000	$ 1,097,110	$ 807,005	$ 656,202
Gross profit	87,500	83,500	76,600	71,500	62,600	59,500	57,300	52,400	49,600	48,900	47,900	42,000	319,091	231,836	188,395
Net income (loss)	$ 14,100	$ 13,100	$ 12,200	$ 11,600	$ 9,200	$ 8,300	$ 7,600	$ 6,300	$ 5,900	$ 5,300	$ 4,600	$ 3,600	$ 50,985	$ 31,437	$ 19,381
Earnings per share - basic (in dollars per share)	$ 0.98	$ 0.91	$ 0.84	$ 0.81	$ 0.64	$ 0.58	$ 0.53	$ 0.44	$ 0.41	$ 0.38	$ 0.33	$ 0.27	$ 3.54	$ 2.19	$ 1.40
Earnings per share - diluted (in dollars per share)	$ 0.92	$ 0.86	$ 0.80	$ 0.77	$ 0.61	$ 0.55	$ 0.50	$ 0.42	$ 0.39	$ 0.36	$ 0.31	$ 0.26	$ 3.35	$ 2.08	$ 1.32