NET INCOME PER COMMON SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
NET INCOME PER COMMON SHARE
Net income	$ 21,659	$ 17,344	$ 45,228	$ 43,365
Shares of common stock outstanding used to compute basic per common share amounts	34,902,103	34,362,757	34,783,419	34,224,756
Effect of dilutive restricted stock units and options (in shares)	499,170	639,594	532,478	592,924
Shares used to compute diluted per common share amounts	35,401,273	35,002,351	35,315,897	34,817,680
Basic income per share (in dollars per share)	$ 0.62	$ 0.50	$ 1.30	$ 1.27
Diluted income per share (in dollars per share)	$ 0.61	$ 0.50	$ 1.28	$ 1.25
Anti-dilutive options (in shares)	0	0	0	0