NET INCOME PER COMMON SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
NET INCOME PER COMMON SHARE
Net income	$ 14,079	$ 17,386	$ 23,569	$ 26,021
Shares of common stock outstanding used to compute basic per common share amounts	34,849,659	34,268,941	34,724,077	34,110,820
Effect of dilutive restricted stock units and options (in shares)	458,038	451,548	501,794	526,949
Shares used to compute diluted per common share amounts	35,307,697	34,720,489	35,225,871	34,637,769
Basic income per share (in dollars per share)	$ 0.40	$ 0.51	$ 0.68	$ 0.76
Diluted income per share (in dollars per share)	$ 0.40	$ 0.50	$ 0.67	$ 0.75
Anti-dilutive options (in shares)	0	0	0	0