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, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	1.40%	1.30%	1.50%
Volatility	23.00%	22.00%	14.00%
Risk-free interest rates	1.96%	2.39%	1.22%
Expected life (years)	1 year	1 year	1 year
Weighted average fair value	$ 17.03	$ 17.49	$ 11.69