Summary of Significant Accounting Policies - Additional Information (Detail) - Stock Repurchase Plan [Member] - USD ($)	9 Months Ended
	Sep. 30, 2019	Nov. 30, 2018
Summary Of Significant Accounting Policy [Line Items]
Available authorized repurchase amount	$ 119,700,000
Stock repurchase plan expiration date	Nov. 19, 2020
Number of common stocks repurchased during the period	218,446,000
Stock repurchased, average costs per share	$ 193.32
Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Stock repurchase plan, authorized amount		$ 150,000,000.0