Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended				6 Months Ended	9 Months Ended		12 Months Ended
	May 31, 2019	Apr. 30, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jul. 31, 2019	May 31, 2018
Class of Stock [Line Items]
Common Stock, Shares Authorized		90,000,000			90,000,000		45,000,000			90,000,000		90,000,000
Proceeds From Issuance Of Common Stock										$ 276,960	$ 159,604
Preferred stock, par value (in dollars per share)					$ 0.0001					$ 0.0001		$ 0.0001
Preferred stock, shares authorized					4,000,000					4,000,000		4,000,000
Series A Junior Participating Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Redesignated of Shares Authorized										200,000
Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues					444,251	3,512,500	874,268	3,450,000
At-Market Equity Program [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues									886,768			3,057,263
Proceeds From Issuance Of Common Stock									$ 59,300			$ 181,200
Value Of Equity Instruments To Be Issued					$ 0					$ 0				$ 250,000
Common stock Average Price									$ 66.83			$ 59.28
At-Market Equity Program Two [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues					444,228
Proceeds From Issuance Of Common Stock					$ 33,000
Gross Amount Remaining To Be Issued										$ 367,000
Common stock Average Price					$ 74.30
At-Market Equity Program Two [Member] | ATM Program [Member] | Common Stock [Member]
Class of Stock [Line Items]
Value Of Equity Instruments To Be Issued													$ 400,000
March 2018 Forward Sale [Member]
Class of Stock [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares				3,450,000
Proceeds From Issuance Of Common Stock			$ 160,200
September 2018 Forward Sales
Class of Stock [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares			3,500,000
Stock Issued During Period, Shares, New Issues			3,500,000
Proceeds From Issuance Of Common Stock	$ 186,000
April 2019 Forward Equity
Class of Stock [Line Items]
Forward Contract Indexed to Issuer's Equity, Shares		3,162,500