Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Value of share equivalents
Market price of Company's stock	$ 78.00	$ 79.10
Phantom Stock and Performance Stock Units
Number of share equivalents
Balance at beginning of the period (in shares)	393,844,000	472,830,000
Granted (in shares)	129,234,000	96,897,000
Forfeited share equivalents (in shares)	(24,460,000)	(5,330,000)
Vested share equivalents (in shares)	(121,758,000)	(143,643,000)
Balance at end of the period (in shares)	376,860,000	420,754,000
Value of share equivalents
Balance at beginning of the period (in shares)	$ 30,523	$ 39,600
Granted (in shares)	10,080	7,665
Forfeited share equivalents (in shares)	(1,908)	(422)
Vested share equivalents (in shares)	(10,187)	(12,024)
Balance at end of the period (in shares)	$ 29,395	$ 33,282