CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 0.9	$ 0.76	$ 0.64
Stock option plan, shares	39,787	13,834	10,964
Employee stock purchase plan, shares	25,136	24,519	24,849
Director stock purchase plan, shares	837
Restricted stock, shares	55,784	54,535	48,816
Treasury Stock, Shares, Retired	870,450	38,032