Shareholders' Equity - Assumptions to Estimate Fair Value of Employee Stock Purchase Rights on Date of Grant Using Black Scholes Option Pricing Model (Detail) - Employee Stock Purchase 2002 Plan - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	1.40%	1.40%	1.30%
Volatility	32.00%	23.00%	22.00%
Risk-free interest rates	0.15%	1.96%	2.39%
Expected life (years)	1 year	1 year	1 year
Weighted average fair value	$ 23.26	$ 17.03	$ 17.49