EMPLOYEE BENEFITS - Summary of RSU and Share Transactions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Stock Units (RSUs)
Units
Beginning balance (in shares)	774,163
Granted (in shares)	208,937
Shares issued (in shares)	(301,938)
Forfeited (in shares)	(6,944)
Ending balance (in shares)	674,218	774,163
Weighted Average Grant-Date Fair Value
Beginning balance (in dollars per share)	$ 54.43
Granted (in dollars per share)	88.23	$ 67.91	$ 56.69
Shares issued (in dollars per share)	57.61
Forfeited (in dollars per share)	60.95
Ending balance (in dollars per share)	$ 63.42	$ 54.43
Performance Shares
Units
Beginning balance (in shares)	486,907
Granted (in shares)	211,224
Shares issued (in shares)	(249,922)
Forfeited (in shares)	(404)
Ending balance (in shares)	447,805	486,907
Weighted Average Grant-Date Fair Value
Beginning balance (in dollars per share)	$ 60.30
Granted (in dollars per share)	75.36	$ 68.33	$ 56.77
Shares issued (in dollars per share)	55.72
Forfeited (in dollars per share)	89.85
Ending balance (in dollars per share)	$ 69.93	$ 60.30