Shareholders' Equity - Summary of Information about Stock Options (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Number of shares - Stock Option
Outstanding Beginning Balance | shares	17,374
Options granted | shares	0
Options exercised | shares	(4,020)
Options forfeited | shares	(328)
Options canceled | shares	(65)
Outstanding Ending Balance | shares	12,961
Exercisable at December 31, 2017 | shares	6,615
Weighted average exercise price per share - Stock Option
Outstanding Beginning Balance | $ / shares	$ 44.25
Options granted | $ / shares	0.00
Options exercised | $ / shares	43.86
Options forfeited | $ / shares	44.23
Options cancelled | $ / shares	46.27
Outstanding Ending Balance | $ / shares	44.36
Exercisable at December 31, 2017 | $ / shares	$ 43.44
Weighted average remaining contractual life - Stock Option
Outstanding at December 31, 2017	5 years 9 months 11 days
Exercisable at December 31, 2017	4 years 3 months 19 days
Aggregate intrinsic value - Stock Option
Outstanding at December 31, 2017 | $	$ 263,431
Exercisable at December 31, 2017 | $	$ 140,569