CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Dividends declared (in dollars per share)	$ 1.88	$ 1.88	$ 1.88
Purchase of treasury stock (in shares)	47,698	14,600	60,018