Dividends (Details) - $ / shares			12 Months Ended
	Oct. 31, 2018	Sep. 29, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common shares, declared	$ 1.02		$ 4.040	$ 3.960	$ 3.840
Common shares, paid			4.020	3.940	3.800
Payments of ordinary dividends, common stock			3.859	3.940	3.800
Common shares, ordinary dividend eligible for 15% rate			$ 0.161	$ 0.000	$ 0.000
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			1.300	1.354	1.354
Preferred shares, ordinary dividend eligible for 15% rate			$ 0.054	$ 0.000	$ 0.000
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	$ 0.368	$ 0.000
Preferred shares, paid			1.306	0.000	0.000
Payment of ordinary dividends, preferred stock			1.254	0.000	0.000
Preferred shares, ordinary dividend eligible for 15% rate			$ 0.052	$ 0.000	$ 0.000