Earnings Per Share - Additional Information (Detail) - shares	1 Months Ended	9 Months Ended	18 Months Ended
	Jul. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jun. 30, 2017	Oct. 31, 2016
Class of Stock [Line Items]
Repurchase of common stock (shares)			0
Class A Common Stock
Class of Stock [Line Items]
Percentage of shares outstanding used in two class method calculation		40.00%
Voting rights		The Class A Common Stock has no voting rights unless four quarterly cumulative dividends upon the Class A Common Stock are in arrears.
Class B Common Stock
Class of Stock [Line Items]
Percentage of shares outstanding used in two class method calculation		60.00%
Voting rights		The Class B Common Stock has full voting rights.
Board Of Director Authorized
Class of Stock [Line Items]
Number of shares authorized to be purchased (shares)	4,703,487	4,703,487		4,000,000
Stock Repurchase Committee Authorized
Class of Stock [Line Items]
Number of shares authorized to be purchased (shares)					110,241
Repurchase of common stock (shares)	2,000