CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 1.1	$ 1.04	$ 0.98
Stock option plan, shares	20,888	30,567	44,067
Employee stock purchase plan, shares	28,996	17,578	23,779
Restricted stock, shares	37,705	47,064	49,468
Treasury Stock, Shares, Retired	0	0	512,459
Director stock purchase plan, shares		258
Number of shares issued by the company, pursuant to WashingtonFirst acquisition	11,446,197