Stock Repurchases (Details) - USD ($)	3 Months Ended	9 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Feb. 06, 2018
Class of Stock [Line Items]
Stock repurchase program, authorized amount			$ 100,000,000
Feb 2018 repurchase program
Class of Stock [Line Items]
Stock repurchased and retired during period (in shares)	574,946	574,946
Stock repurchase, price paid per share (in dollars per share)	$ 173.91	$ 173.91
Total cost of stock repurchased, net	$ 100,000,000	$ 100,000,000