STOCK-BASED COMPENSATION - Stock option activity (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Number of Shares
Beginning balance (in shares) | shares	369,483
Exercised (in shares) | shares	348,469
Ending balance (in shares) | shares	21,014
Weighted Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 26.40
Exercised (in dollars per share) | $ / shares	26.77
Ending balance (in dollars per share) | $ / shares	$ 20.24
Weighted Average Remaining Contractual Term (years)
Outstanding	6 months
Aggregate Intrinsic Value (in millions)
Ending balance | $	$ 2.0