CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Dividends paid to public stockholders (per share)	$ 0.850	$ 0.780	$ 0.693
Dividends paid to affiliate (per share)	$ 0.850	$ 0.780	$ 0.693