SHARE-BASED AWARDS AND OPTIONS (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Compensation Cost , Allocation of Share-based Compensation Costs by Plan

The following table summarizes share-based compensation expense and the related income tax benefit recognized for our share-based awards and stock options:



	Year Ended December 31,				Seven Months Ended December 31,		Year Ended May 31,
	2018		2017		2016		2016

	(in thousands)
Share-based compensation expense	$	57,826	$	39,095	$	18,707	$	30,809
Income tax benefit	$	13,038	$	13,849	$	6,582	$	9,879

Schedule of Changes in Non-Vested Restricted Stock Awards Activity

The following table summarizes the changes in unvested restricted stock and performance awards for the years ended December 31, 2018 and 2017, the 2016 fiscal transition period and the year ended May 31, 2016:



	Shares		Weighted-Average Grant-Date Fair Value
	(in thousands)
Unvested at May 31, 2015	1,848			$28.97
Granted	461		57.04
Vested	(633	)	27.55
Forfeited	(70	)	34.69
Unvested at May 31, 2016	1,606		37.25
Granted	348		74.26
Vested	(639	)	31.38
Forfeited	(52	)	45.27
Unvested at December 31, 2016	1,263		49.55
Granted	899		79.79
Vested	(858	)	39.26
Forfeited	(78	)	59.56
Unvested at December 31, 2017	1,226		78.29
Granted	650		109.85
Vested	(722	)	60.08
Forfeited	(70	)	91.47
Unvested at December 31, 2018	1,084			$108.51

Schedule of Share-based Compensation, Stock Options, Activity

The following table summarizes changes in stock option activity for the years ended December 31, 2018 and 2017, the 2016 fiscal transition period and the year ended May 31, 2016:



	Options		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value
	(in thousands)				(years)	(in millions)
Outstanding at May 31, 2015	894			$25.47	5.2		$23.9
Granted	145		55.92
Forfeited	(8	)	16.10
Exercised	(220	)	22.46			9.4
Outstanding at May 31, 2016	811		31.81		5.8	36.8
Granted	73		74.66
Forfeited	(1	)	22.93
Exercised	(124	)	22.26			6.5
Outstanding at December 31, 2016	759		37.51		6.0	24.5
Granted	124		79.45
Forfeited	—		—
Exercised	(160	)	23.50			10.1
Outstanding at December 31, 2017	723		47.79		6.4	37.9
Granted	103		114.70
Forfeited	(22	)	100.38
Exercised	(206	)	42.65			16.5
Outstanding at December 31, 2018	598			$59.16	6.2		$27.3

Options vested and exercisable at December 31, 2018	427			$44.34	5.2		$25.1

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

Fair value was estimated on the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions:



	Year Ended December 31,				Seven Months Ended December 31,		Year Ended May 31,
	2018		2017		2016		2016
Risk-free interest rate	2.60	%	1.99	%	1.05	%	1.62	%
Expected volatility	29	%	30	%	32	%	29	%
Dividend yield	0.04	%	0.06	%	0.06	%	0.10	%
Expected term (years)	5		5		5		5