Consolidated Statements of Equity (Parenthetical) - $ / shares			3 Months Ended		12 Months Ended
	Dec. 30, 2016	Dec. 13, 2016	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Dividends declared per common share	$ 1.90	$ 1.90	$ 0.375	$ 0.375	$ 1.65	$ 3.375	$ 1.40