Shareholders' Equity - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 01, 2017	Aug. 31, 2015	Dec. 31, 2012
Equity [Abstract]
Dividends declared per share (in dollars per share)	$ 2.66	$ 2.40	$ 2.06
Dividends payable	$ 54,420,000	$ 50,678,000	$ 44,800,000
Dividend per share declared (in dollars per share)	$ 0.69	$ 0.64	$ 0.56
Shares authorized under repurchase program						$ 250,000,000
Stock repurchase program, value	$ 300,000,000
Remaining authorized amended repurchase amount	56,100,000
Additional authorized amount				$ 250,000,000	$ 250,000,000
Remaining authorized repurchase amount	$ 295,100,000
Remaining number of shares authorized to be repurchase	1,933,959
Stock repurchased during period as percentage of shares outstanding	2.40%
Shares repurchased (in shares)	459,264	1,058,018.000	1,074,210.00
Shares repurchased, average price per share (in dollars per share)	$ 126.44	$ 124.01	$ 114.90
Shares repurchased, amount	$ 58,069,000	$ 127,443,000	$ 121,193,000