CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 0.98	$ 0.9	$ 0.76
Stock option plan, shares	44,067	39,787	13,834
Director stock purchase plan, shares	258	837
Employee stock purchase plan, shares	23,779	25,136	24,519
Restricted stock, shares	49,468	55,784	54,535
Treasury Stock, Shares, Retired	512,459	870,450	38,032