Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Cash dividends declared per common share (in dollars per share)	$ 0.81	$ 0.70	$ 0.62
Common stock issued, price per share (in dollars per share)	$ 44.26	$ 32.45	$ 34.32