CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Statement of Stockholders' Equity [Abstract]
Cumulative dividends declared per common share	$ 0.38	$ 0.25	$ 1.58	$ 1.75	$ 2.00