STOCK-BASED COMPENSATION - Stock option activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Weighted Average Exercise Price
Cash received in exercise of share options	$ 250	$ 17
Stock option plans
Number of Shares Underlying Options
Outstanding, beginning of period	260,322	248,314
Granted		80,000
Forfeited		(12,160)
Exercised	(25,400)	(1,000)
Outstanding, end of period	234,922	315,154
Weighted Average Exercise Price
Outstanding, beginning of period	$ 16.00	$ 12.80
Granted		21.00
Forfeited		11.24
Exercised	9.85	16.80
Outstanding, end of period	$ 16.67	$ 14.93

Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Weighted average price of options that were either forfeited or expired.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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