Equity - Dividends on Common Stock (Details) - $ / shares	3 Months Ended												12 Months Ended
	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
Equity [Abstract]
Dividends declared (usd per share)	$ 0.205	$ 0.205	$ 0.205	$ 0.205	$ 0.185	$ 0.185	$ 0.185	$ 0.185	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.82	$ 0.74	$ 0.68
Dividends payment date	Jan. 15, 2019	Oct. 15, 2018	Jul. 13, 2018	Apr. 13, 2018	Jan. 16, 2018	Oct. 13, 2017	Jul. 14, 2017	Apr. 14, 2017	Jan. 13, 2017	Oct. 14, 2016	Jul. 15, 2016	Apr. 15, 2016