PREFERRED STOCK - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended									12 Months Ended
	Sep. 15, 2015	Nov. 30, 2017	Sep. 30, 2017	Aug. 31, 2017	Jun. 30, 2017	May 31, 2017	Apr. 30, 2017	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred stock, authorized (in shares)											1,000,000	1,000,000
Preferred stock, issued (in shares)											673,380	726,500
Preferred stock, outstanding (in shares)											673,380	726,500
Depositary shares (in shares)	7,700,000
Preferred stock, dividend rate	5.25%
Preferred stock, par value (in dollars per share)	$ 0.01										$ 0.01	$ 0.01
Gross proceeds from issuance of preferred stock	$ 770.0
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Depositary Shares, Liquidation Preference Per Share	$ 100.00
Dividends paid on mandatory convertible preferred stock											$ 36.3	$ 39.4	$ 10.1
Increase to retained earnings on repurchase of mandatory convertible preferred stock											$ 17.3	$ 11.3	$ 0.0
Depositary shares repurchased during period (in shares)		65,000	25,000	120,000	35,000	65,000	75,500	5,006	40,694	100,000	531,200
Depository shares equivalent to preferred stock units (in shares)											53,120
Minimum
Class of Stock [Line Items]
Common stock issuable upon conversion (in shares)	5.8716
Maximum
Class of Stock [Line Items]
Common stock issuable upon conversion (in shares)	7.3394
Preferred Stock
Class of Stock [Line Items]
Issuance of preferred stock (in dollars per share)	$ 100.00