Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Changes in Stockholders' Equity [Abstract]
Cash dividends - per share (in dollars per share)	$ 0.92	$ 0.90	$ 0.87
Purchase of treasury shares (in shares)	0	675,535	1,047,152
Net issuance of shares to employee and other stock plans, including tax benefit for 2016 and 2015 (in shares)	285,059	502,585	581,400