INCENTIVE PLANS - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options (in shares):
Outstanding, beginning of period (in shares)	1,138,813	1,527,396	6,656,588
Canceled (in shares)	0	0	(25,334)
Expired (in shares)	(376,588)	0	(2,613,909)
Exercised (in shares)	0	(388,583)	(2,489,949)
Outstanding, end of period (in shares)	762,225	1,138,813	1,527,396
Exercisable, end of period	762,225	1,138,813	1,527,396
Weighted- average exercise price (in dollars per share):
Outstanding, beginning of period (in dollars per share)	$ 161.96	$ 131.78	$ 67.92
Canceled (in dollars per share)	0.00	0.00	40.80
Expired (in dollars per share)	283.63	0.00	48.80
Exercised (in dollars per share)	0.00	43.35	49.10
Outstanding, end of period (in dollars per share)	101.84	161.96	131.78
Intrinsic value per share (in dollars per share):
Outstanding (in dollars per share)	0.00	0.00	0.00	$ 0.00
Exercised (in dollars per share)	$ 0.00	$ 15.67	$ 6.60
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period	6 years