Equity (Details 1) - $ / shares	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
6.50% Series C [Member]
Dividends on preferred shares/units
Dividend per Share (usd per share)	$ 0.41	$ 0.41	$ 0.41	$ 0.41
Record Date	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Payable Date	Jan. 12, 2018	Oct. 16, 2017	Jul. 17, 2017	Apr. 17, 2017
6.375% Series D [Member]
Dividends on preferred shares/units
Dividend per Share (usd per share)	$ 0.40	$ 0.40	$ 0.40	$ 0.40
Record Date	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Payable Date	Jan. 12, 2018	Oct. 16, 2017	Jul. 17, 2017	Apr. 17, 2017