Treasury Stock - Additional Information (Detail)	21 Months Ended
	Sep. 30, 2018 expansion	Feb. 21, 2018 USD ($)	Nov. 04, 2015 USD ($)
Equity [Abstract]
Stock repurchase program authorized amount (up to) | $		$ 300,000,000	$ 50,000,000
Number of expansions to stock repurchase program | expansion	2