NET INCOME PER COMMON SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Numerator:
Income from continuing operations	$ 101,130	$ 80,604	$ 61,569
Income from discontinued operations	0	9,906	7,047
Net income	$ 101,130	$ 90,510	$ 68,616
Denominator:
Denominator for basic calculation-weighted-average common shares	80,323,000	81,615,000	86,716,000
Weighted-average effect of dilutive securities	1,166,000	719,000	494,000
Denominator for diluted calculation	81,489,000	82,334,000	87,210,000
Net income per common share:
Basic income from continuing operations	$ 1.26	$ 0.99	$ 0.71
Basic income from discontinued operations	$ 0.00	$ 0.12	$ 0.08
Basic net income	$ 1.26	$ 1.11	$ 0.79
Diluted income from continuing operations	$ 1.24	$ 0.98	$ 0.71
Diluted income from discontinued operations	$ 0.00	$ 0.12	$ 0.08
Diluted net income	$ 1.24	$ 1.10	$ 0.79
Stock Compensation Plan [Member]
Antidilutive Securities [Abstract]
Antidilutive shares excluded from the diluted net income per common share computation	600,000	1,900,000	2,800,000