Equity - Dividends on Common Stock (Details) - $ / shares	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Equity [Abstract]
Dividends declared per common share (in usd per share)	$ 0.205	$ 0.205	$ 0.185	$ 0.41	$ 0.37	$ 0.74
Dividend payable date	Jul. 13, 2018	Apr. 13, 2018