Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Value of share equivalents
Market price of Company's stock	$ 75.80	$ 81.5
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)	140,804,000	105,048,000
Forfeited share equivalents (in shares)	(45,821,000)	(15,104,000)
Vested share equivalents (in shares)	(126,019,000)	(150,409,000)
Balance at end of the period (in shares)	362,808,000	412,365,000
Value of share equivalents
Balance at beginning of the period (in shares)	$ 30,523	$ 39,600
Granted (in shares)	10,673	8,561
Forfeited share equivalents (in shares)	(3,473)	(1,231)
Vested share equivalents (in shares)	(10,519)	(12,555)
Balance at end of the period (in shares)	$ 27,501	$ 33,608