Basic and Diluted Earnings Per Share - Numerator and Denominator of the Basic and Diluted Per Share Computations for Earnings Attributable to Shareholders Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Earnings Attributable to Shareholders
Basic earnings attributable to shareholders									$ 489,345	$ 430,807	$ 457,223
Diluted earnings attributable to shareholders									$ 489,345	$ 430,807	$ 457,223
Weighted Average Shares
Weighted average basic shares outstanding									179,247	181,282	188,941
Effect of dilutive potential common shares									2,419	1,422	1,282
Weighted average diluted shares outstanding									181,666	182,704	190,223
Earnings Per Share
Basic earnings attributable to shareholders per share	$ 0.94	$ 0.67	$ 0.60	$ 0.52	$ 0.61	$ 0.59	$ 0.64	$ 0.53	$ 2.73	$ 2.38	$ 2.42
Diluted earnings attributable to shareholders per share	$ 0.92	$ 0.66	$ 0.60	$ 0.51	$ 0.61	$ 0.59	$ 0.63	$ 0.53	$ 2.69	$ 2.36	$ 2.40