NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Share Repurchase Program (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Nov. 07, 2018	Sep. 30, 2018	Sep. 30, 2018	Aug. 09, 2018	Sep. 06, 2016
Class of Stock [Line Items]
Stock repurchase program, authorized amount					$ 150.0
Stock repurchase program, additional authorized repurchase amount				$ 1,000.0
Class A Common Stock
Class of Stock [Line Items]
Treasury stock, shares acquired (in shares)		1.6	1.6
Treasury stock, value acquired		$ 45.9	$ 45.9
Subsequent Event
Class of Stock [Line Items]
Treasury stock, shares acquired (in shares)	3.4
Treasury stock, value acquired	$ 96.7
Stock repurchase program, remaining authorized repurchase amount	$ 946.4