CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 1.18	$ 1.10	$ 1.04
Stock option plan, shares	15,080	20,888	30,567
Employee stock purchase plan, shares	37,091	28,996	17,578
Restricted stock, shares	54,789	38,360	47,064
Director stock purchase plan, shares	867
Number of shares issued by the company, pursuant to WashingtonFirst acquisition		11,446,197