Subsequent Events - Common Stock Dividend (Details) - $ / shares			3 Months Ended									12 Months Ended
	Feb. 21, 2018	Nov. 01, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Quarterly dividend of common stock declared (in dollars per share)		$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.1375	$ 0.55	$ 0.55	$ 0.28
Annualized dividend rate (in dollars per share)						$ 0.55				$ 0.55		$ 0.55	$ 0.55	$ 0.55
Subsequent Event [Member]
Subsequent Event [Line Items]
Quarterly dividend of common stock declared (in dollars per share)	$ 0.1375
Annualized dividend rate (in dollars per share)	$ 0.55