EARNINGS PER SHARE (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator for basic and diluted earnings per share:
Net income	$ 28,672	$ 22,902	$ 37,632	$ 33,404
Denominator:
Basic shares outstanding	60,665	60,550	60,695	60,507
Dilutive effect of equity-based compensation awards (in shares)	113	137	127	151
Dilutive shares outstanding	60,778	60,687	60,822	60,658
Basic earnings per share (in USD per share)	$ 0.47	$ 0.38	$ 0.62	$ 0.55
Diluted earnings per share (in USD per share)	$ 0.47	$ 0.38	$ 0.62	$ 0.55