EMPLOYEE BENEFIT PLANS - 401(k) Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Employee contribution, maximum percentage of eligible annual compensation	25.00%
Maximum annual contribution by employee	$ 18,500
Minimum age required to be eligible to make catch-up contribution	50 years
Maximum additional contribution over and above regular annual contribution limits	$ 6,000
Maximum employer matching contribution (as a percent)	4.00%
Expenses recorded due to adopting a cash match for employee contributions to the 401(k) plan	$ 9,200,000	$ 8,200,000
Amount of expenses recorded under a plan that provides supplemental matching contributions in excess of limits imposed	$ 1,300,000	$ 1,100,000	$ 600,000