Subsequent Events - Common Stock Dividend (Details) - $ / shares		3 Months Ended												12 Months Ended
	Feb. 20, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 19, 2019
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	$ 0.1375	$ 0.1375	$ 0.55	$ 0.55	$ 0.55
Annualized dividend rate (in dollars per share)		$ 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