EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
SHARE-BASED COMPENSATION
Net income	$ 15,193	$ 11,812	$ 43,694	$ 36,916
Weighted average shares outstanding - basic	29,297,465	30,300,195	29,536,536	30,526,260
Weighted average shares outstanding - diluted	29,479,812	30,514,459	29,743,238	30,758,989
Basic earnings per common share (in dollars per share)	$ 0.52	$ 0.39	$ 1.48	$ 1.21
Diluted earnings per common share (in dollars per share)	$ 0.52	$ 0.39	$ 1.47	$ 1.20
Antidilutive securities excluded from the dilutive share calculation (in shares)	0	80	0	8
Stock Option
SHARE-BASED COMPENSATION
Dilutive effect of share-based compensation arrangements	182,347	214,264	206,702	232,729

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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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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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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