CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 0.48	$ 0.44
Stock option plan, shares	28,941	26,695
Employee stock purchase plan, shares	12,471	12,613
Director stock purchase plan, shares	258	837
Restricted stock, shares	49,648	52,921
Treasury Stock, Shares, Retired	512,459	575,472