Summary of Nonvested Restricted Shares Activity (Detail) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
GRANT DATE FAIR VALUE
Nonvested awards outstanding, beginning balance | $ / shares	$ 63.85	[1]
Granted | $ / shares	64.34	[1]
Vested | $ / shares	62.56	[1]
Nonvested awards outstanding, ending balance | $ / shares	$ 65.92	[1]
NONVESTED NUMBER OF SHARES
Nonvested awards outstanding, beginning balance | shares	189,500
Granted | shares	147,100
Vested | shares	(186,100)
Nonvested awards outstanding, ending balance | shares	150,500

[1] Weighted Average