Shareholders' Equity - Narrative (Details) - USD ($)		9 Months Ended
	Nov. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Nov. 14, 2017	Sep. 30, 2017	Mar. 28, 2016
Class of Stock [Line Items]
Common stock authorized (in shares)		200,000,000			200,000,000
Net proceeds from equity offering		$ 395,092,000	$ 98,755,000
Shelf Registration Statement
Class of Stock [Line Items]
Debt and equity securities authorized for issuance						$ 2,500,000,000
Debt and equity securities authorized for issuance value remaining		$ 650,000,000
At-The-Market
Class of Stock [Line Items]
Value of shares authorized for issuance				$ 500,000,000
Common stock sold (in shares)		0
Underwriting Agreement
Class of Stock [Line Items]
Common stock authorized (in shares)	4,558,404
Gross proceeds from equity offering	$ 400,000,000
Net proceeds from equity offering	$ 395,100,000