Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Parenthetical) (Detail)	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%	100.00%