Equity and Mezzanine Securities Equity and Mezzanine Securities, Schedule of Sale of Common Stock (Details) - USD ($)		1 Months Ended			3 Months Ended			6 Months Ended
	Mar. 30, 2016	May 31, 2017	Sep. 30, 2016	Jun. 30, 2015	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Jun. 30, 2017
Aggregate Value of Shares to be Issued in Accordance to Sales Agreement				$ 225,000,000				$ 250,000,000.0
Share Price	$ 66.50						$ 66.50
Proceeds from Issuance of Common Stock	$ 385,400,000	$ 408,900,000	$ 283,600,000				$ 385,400,000
New shares issued (in shares)	6,037,500	4,830,000	3,737,500		400,000,000	280,502,000	6,037,500
Shares Issued, Price Per Share		$ 86.00	$ 76.50
Shares Issued, Weighted Average Price Per Share					$ 85.01	$ 76,470		$ 85.01
Issuance of OP units and common stock, net					$ 0	$ 21,200		$ 461,248,000