NET INCOME PER COMMON SHARE - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income	$ 10,814	$ 47,187	$ 16,773	$ 57,552
Adjustment for Basic EPS:
Earnings allocated to unvested shareholders	(122)	(727)	(217)	(972)
Adjusted net income	$ 10,692	$ 46,460	$ 16,556	$ 56,580
Denominator:
Weighted average common shares outstanding – Basic	46,868,999	46,742,746	46,826,314	46,702,376
Effect of dilutive shares:
Common stock equivalents arising from stock options and ESPP	709	1,450	1,237	2,324
Restricted stock awards and units and performance units	31,390	66,042	45,558	76,420
Weighted average common shares outstanding – Diluted	46,901,098	46,810,238	46,873,109	46,781,120
Basic	$ 0.23	$ 0.99	$ 0.35	$ 1.21
Diluted	$ 0.23	$ 0.99	$ 0.35	$ 1.21

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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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