EARNINGS PER SHARE (Details) (USD $) In Thousands, except 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, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net income	$ 62,084	$ 64,765	$ 66,319	$ 64,243	$ 57,733	$ 55,530	$ 57,013	$ 46,910	$ 257,411	$ 217,186	$ 130,244
Denominator:
Basic weighted average shares outstanding (in shares)									83,087,000	83,681,000	84,407,000
Effect of dilutive securities - stock options and awards (in shares)									1,088,000	1,027,000	816,000
Diluted weighted average shares outstanding (in shares)									84,175,000	84,708,000	85,223,000
Basic earnings per share (in dollars per share)	$ 0.75	$ 0.78	$ 0.80	$ 0.77	$ 0.69	$ 0.66	$ 0.69	$ 0.56	$ 3.10	$ 2.60	$ 1.54
Diluted earnings per share (in dollars per share)	$ 0.74	$ 0.77	$ 0.79	$ 0.76	$ 0.68	$ 0.66	$ 0.68	$ 0.55	$ 3.06	$ 2.56	$ 1.53
Anti-dilutive shares excluded from the computation of diluted earnings per share									107,814	626,135	1,504,346