STOCK-BASED COMPENSATION- Nonvested options activity (Details) - Stock options	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Options
Beginning balance (in shares) | shares	81,068
Vested (in shares) | shares	(40,533)
Ending balance (in shares) | shares	40,535
Weighted Average Grant-Date Fair Value
Beginning balance (in USD per share) | $ / shares	$ 49.17
Vested (in USD per share) | $ / shares	49.17
Ending balance (in USD per share) | $ / shares	$ 49.17