CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - UNAUDITED - (Parenthetical) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Stockholders Equity [Abstract]
Common stock dividends, per share	$ 0.30	$ 0.28	$ 0.88	$ 0.82
Stock option plan, shares	1,325	1,991	12,222	19,918
Employee stock purchase plan, shares	9,544	7,607	27,210	21,428
Restricted stock, shares			54,789	37,705
Director stock purchase plan, shares			867
Number of shares issued by the company, pursuant to WashingtonFirst acquisition				11,446,197