EARNINGS PER SHARE (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator for basic and diluted earnings per share:
Net income	$ 22,902	$ 23,426	$ 33,404	$ 55,441
Denominator:
Basic shares outstanding	60,550	53,308	60,507	53,268
Dilutive effect of equity-based compensation awards (in shares)	137	197	151	229
Dilutive shares outstanding	60,687	53,505	60,658	53,497
Basic earnings per share:
Basic earnings per share (in USD per share)	$ 0.38	$ 0.44	$ 0.55	$ 1.04
Diluted earnings per share:
Diluted earnings per share (in USD per share)	$ 0.38	$ 0.44	$ 0.55	$ 1.04

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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