Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Repurchase and retirement of common stock	$ 200	$ 500	$ 48,800	$ 500	$ 400	$ 6,200	$ 49,500
Repurchase and retirement of common stock (shares)							600,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	2,600,000						2,600,000
Cash dividend paid during period, per share (in dollars per share)	$ 0.62			$ 0.61			$ 1.86	$ 1.83
Common stock excluded from calculation of diluted earnings per share (shares)	2,200,000			4,300,000			5,000,000.0	4,200,000
Omnibus Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock excluded from calculation of diluted earnings per share (shares)							700,000