Share-Based Compensation - Summary of Transactions Involving Performance Awards (Detail) - $ / shares shares in Thousands	7 Months Ended	12 Months Ended
	Dec. 31, 2015	May. 31, 2015	May. 31, 2014	May. 31, 2013
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term performance stock units, beginning of year	28	50	57	64
Granted			17	19
Vested and settled	(15)	(22)	(24)	(26)
Cancelled	0	0	0	0
Long-term performance stock units, end of year	13	28	50	57
Long-term performance stock units, beginning of year, Weighted Average Fair Value	$ 32.86	$ 30.63	$ 25.47	$ 21.86
Granted, Weighted Average Fair Value			36.40	32.89
Vested and settled, Weighted Average Fair Value	30.82	27.66	22.65	22.04
Cancelled, Weighted Average Fair Value	0	0	0	0
Long-term performance stock units, end of year, Weighted Average Fair Value	$ 35.15	$ 32.86	$ 30.63	$ 25.47
Long Term Performance Stock Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Long-term performance stock units, beginning of year	23
Granted	36	23
Cancelled	0	0
Long-term performance stock units, end of year	59	23
Long-term performance stock units, beginning of year, Weighted Average Fair Value	$ 42.25
Granted, Weighted Average Fair Value	33.91	$ 42.25
Cancelled, Weighted Average Fair Value	0	0
Long-term performance stock units, end of year, Weighted Average Fair Value	$ 37.16	$ 42.25