Shareholders' Equity - Narrative (Details) - USD ($)		3 Months Ended
	Nov. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Nov. 19, 2018	Nov. 13, 2018
Class of Stock [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares		339,574
Stock issued during period, new issues (in shares)		2,720,060
Net proceeds from equity offering		$ 259,005,000	$ 494,734,000
Forward sales equity agreement, forward rate per share		$ 107.40
Shelf Registration Statement
Class of Stock [Line Items]
Debt and equity securities authorized for issuance					$ 3,000,000,000.0
Debt and equity securities authorized for issuance value remaining		$ 500,000,000
At-The-Market
Class of Stock [Line Items]
Value of shares authorized for issuance				$ 500,000,000
Forward Contract Indexed to Issuer's Equity, Shares		339,574
Value of shares available for issuance		$ 38,000,000
Stock issued during period, new issues (in shares)		2,234,871
Net proceeds from equity offering		$ 214,600,000
Forward contract indexed to issuer's equity, settlement alternatives, cash, at fair value		$ 36,800,000
Common Stock Block Trade
Class of Stock [Line Items]
Stock issued during period, new issues (in shares)	5,390,836
Gross proceeds from equity offering	$ 500,000,000
Net proceeds from equity offering	$ 494,100,000
Forward Sales Equity Agreements
Class of Stock [Line Items]
Stock issued during period, new issues (in shares)		485,189	2,668,464
Net proceeds from equity offering		$ 44,400,000
Forward contract indexed to issuer's equity, settlement alternatives, cash, at fair value		$ 239,600,000	$ 247,500,000
Forward sales equity agreement, forward rate per share		$ 106.51