Shareholders' Equity - Additional Information (Detail)		12 Months Ended
	Jul. 11, 2016	Sep. 30, 2017
Class of Stock [Line Items]
Stock split ratio		1.5
Common Stock [Member]
Class of Stock [Line Items]
Right of holders to elect company's board of directors		25.00%
Class B Stock [Member]
Class of Stock [Line Items]
Right of holders to elect company's board of directors		75.00%
Common and Class B Stock [Member]
Class of Stock [Line Items]
Stock split ratio	1.5
Stock dividend percentage	50.00%
Stock split ratio description		On July 11, 2016, the Company's Board of Directors approved a three-for-two split of the Company's common and Class B stock to be effected in the form of a 50% stock dividend. As a result, shareholders received one additional share of common or Class B stock for every two shares they held of the respective class of stock as of the record date.