Subsequent Events - Additional Information (Detail) - Subsequent Event [Member]	Oct. 23, 2018 $ / shares
Dividend Declared [Member]
Subsequent Event [Line Items]
Date of declared to shareholders entitled to dividends	Oct. 23, 2018
Cash dividend per share	$ 0.22
Date of payment to shareholders entitled to dividends	Dec. 28, 2018
Date of record of shareholders entitled to dividends	Dec. 14, 2018
Extraordinary Dividend Declared [Member]
Subsequent Event [Line Items]
Date of declared to shareholders entitled to dividends	Oct. 23, 2018
Cash dividend per share	$ 3.50
Date of payment to shareholders entitled to dividends	Dec. 28, 2018
Date of record of shareholders entitled to dividends	Dec. 14, 2018