CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 0.72	$ 0.66
Stock option plan, shares	34,646	35,039
Employee stock purchase plan, shares	18,767	19,377
Director stock purchase plan, shares	258	837
Restricted stock, shares	49,648	53,746
Treasury Stock, Shares, Retired	512,459	728,932