CAPITAL STOCK AND SHARE-BASED COMPENSATION - Non-Vested Stock Option Activity (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number of Shares
Non-vested stock options beginning balance (shares) | shares	726,699
Granted (shares) | shares	308,292
Vested (shares) | shares	(260,814)
Forfeited (shares) | shares	(246,379)
Non-vested stock options ending balance (shares) | shares	527,798
Weighted Average Exercise Price
Non-vested stock options beginning balance (usd per share) | $ / shares	$ 32.58
Granted (usd per share) | $ / shares	43.13
Vested (usd per share) | $ / shares	30.54
Forfeited (usd per share) | $ / shares	39.48
Non-vested stock options ending balance (usd per share) | $ / shares	$ 36.52