Subsequent Events (Details) - $ / shares			3 Months Ended				12 Months Ended
	Feb. 21, 2019	Feb. 01, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Cash dividends declared per common share (in $ per share)			$ 0.55	$ 0.55	$ 0.45	$ 0.45	$ 2	$ 1.80	$ 1.8
Cash dividends declared per preferred share (in $ per share)			$ 1.8125	$ 1.8125	$ 1.8125	$ 1.8125	$ 7.25	$ 7.25	$ 0
Subsequent Event
Subsequent Event [Line Items]
Cash dividends declared per common share (in $ per share)	$ 0.55
Cash dividends declared per preferred share (in $ per share)	$ 1.8125
Convertible preferred stock
Subsequent Event [Line Items]
Preferred stock dividend rate		7.25%