CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - UNAUDITED - (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 0.30	$ 0.28	$ 0.58	$ 0.54
Stock option plan, shares	4,142	5,574	10,897	17,927
Employee stock purchase plan, shares	10,004	6,909	17,666	13,821
Restricted stock, shares	42,830	36,191	54,789	37,705
Director stock purchase plan, shares	867		867
Number of shares issued by the company, pursuant to WashingtonFirst acquisition		11,446,197		11,446,197