EMPLOYEE BENEFITS - Stock Ownership and Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Stock Ownership, 401(K) And Deferred Compensation Plan
Annual expenses for incentive plans	$ 11.9	$ 19.7	$ 19.2
ESOP and 401(k) Plans
Employee Stock Ownership, 401(K) And Deferred Compensation Plan
Vesting period of profit sharing contributions	3 years
Expenses recognized	$ 8.8	$ 12.5	$ 11.7
Employee Stock Ownership Plan (ESOP)
Employee Stock Ownership, 401(K) And Deferred Compensation Plan
Shares purchased under defined contribution plan	98,717	124,186	112,608
Average price of shares purchased (in dollars per share)	$ 62.80	$ 58.02	$ 64.20
Aggregate price of shares purchased	$ 6.2	$ 7.2	$ 7.2
Shares held by the ESOP	2,985,390
Employee 401(k) Plans
Employee Stock Ownership, 401(K) And Deferred Compensation Plan
Employer contribution as a percent of eligible compensation	3.00%
Vesting percentage in basic and voluntary contributions	100.00%
Deferred compensation plan
Employee Stock Ownership, 401(K) And Deferred Compensation Plan
Shares purchased under defined contribution plan	7,049	7,464	6,702
Average price of shares purchased (in dollars per share)	$ 68.36	$ 58.66	$ 61.61
Aggregate price of shares purchased	$ 0.5	$ 0.4	$ 0.4
Assets held under trust	$ 36.2