Dividends (Details) - $ / shares			12 Months Ended
	Oct. 30, 2019	Sep. 29, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred shares, percentage			5.00%	5.00%	5.00%
Common shares, declared	$ 1.05		$ 4.140	$ 4.040	$ 3.960
Common shares, paid			4.110	4.020	3.940
Payments of ordinary dividends, common stock			4.110	3.859	3.940
Common shares, ordinary dividend eligible for 15% rate			$ 0	$ 0.161	$ 0
Common shares, qualified dividends, tax rate			15.00%	15.00%	15.00%
Preferred stock, qualified dividends, tax rate			15.00%	15.00%	15.00%
5.417% Series 1 Cumulative Convertible Preferred Shares
Class of Stock [Line Items]
Preferred shares, percentage			5.417%	5.417%	5.417%
Preferred shares, declared			$ 1.354	$ 1.354	$ 1.354
Preferred shares, paid			1.354	1.354	1.354
Payment of ordinary dividends, preferred stock			1.354	1.300	1.354
Preferred shares, ordinary dividend eligible for 15% rate			$ 0	$ 0.054	$ 0
5.0% Series C Cumulative Redeemable Preferred Shares
Class of Stock [Line Items]
Preferred shares, percentage		5.00%	5.00%	5.00%	5.00%
Preferred shares, declared			$ 1.250	$ 1.250	$ 0.368
Preferred shares, paid			1.250	1.306	0
Payment of ordinary dividends, preferred stock			1.250	1.254	0
Preferred shares, ordinary dividend eligible for 15% rate			$ 0	$ 0.052	$ 0