NET INCOME PER COMMON SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
NET INCOME PER COMMON SHARE
Net income	$ 17,344	$ 15,412	$ 42,285	$ 37,056
Shares of common stock outstanding used to compute basic per common share amounts	34,362,757	33,571,967	34,224,756	33,477,951
Effect of dilutive restricted stock and options (in shares)	639,594	775,248	592,924	737,154
Shares used to compute diluted per common share amounts	35,002,351	34,347,215	34,817,680	34,215,105
Basic income per share (in dollars per share)	$ 0.50	$ 0.46	$ 1.24	$ 1.11
Diluted income per share (in dollars per share)	$ 0.50	$ 0.45	$ 1.21	$ 1.08