Consolidated Statements of Income - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income
Loans, including fees	$ 145,816,000	$ 131,763,000	$ 116,816,000
Securities, taxable	7,919,000	6,736,000	5,326,000
Securities, tax-exempt	2,231,000	2,239,000	2,305,000
Other interest-earning assets	2,371,000	1,243,000	1,096,000
Total interest income	158,337,000	141,981,000	125,543,000
Interest expense
Deposits	21,264,000	13,869,000	9,362,000
Short-term borrowings	295,000	273,000	190,000
Federal Home Loan Bank advances	8,977,000	4,647,000	3,657,000
Subordinated debentures and other borrowings	3,267,000	3,110,000	2,586,000
Total interest expense	33,803,000	21,899,000	15,795,000
Net interest income	124,534,000	120,082,000	109,748,000
Provision for loan losses	1,750,000	1,100,000	2,950,000
Net interest income after provision for loan losses	122,784,000	118,982,000	106,798,000
Noninterest income:
Mortgage banking activities	8,485,000	4,109,000	4,421,000
Payroll processing	1,626,000	1,462,000	1,305,000
Earnings on bank owned life insurance	3,886,000	1,287,000	2,731,000
Letter of credit fees	278,000	245,000	348,000
Other income	2,172,000	2,195,000	1,203,000
Total noninterest income	26,956,000	19,010,000	19,001,000
Noninterest expense
Salaries and benefits	53,833,000	50,910,000	45,397,000
Occupancy	7,061,000	6,711,000	6,186,000
Furniture and equipment rent, depreciation and maintenance	2,583,000	2,470,000	2,168,000
Data processing	9,235,000	8,557,000	8,222,000
Advertising	1,446,000	1,648,000	1,608,000
FDIC insurance costs	225,000	930,000	960,000
Problem asset costs	140,000	90,000	355,000
Other expense	14,757,000	14,854,000	14,820,000
Total noninterest expenses	89,280,000	86,170,000	79,716,000
Income before federal income tax expense	60,460,000	51,822,000	46,083,000
Federal income tax expense	11,004,000	9,798,000	14,809,000
Net income	$ 49,456,000	$ 42,024,000	$ 31,274,000
Earnings per common share:
Basic (in dollars per share)	$ 3.01	$ 2.53	$ 1.90
Diluted (in dollars per share)	$ 3.01	$ 2.53	$ 1.90
Deposit Account [Member]
Noninterest income:
Noninterest income	$ 4,584,000	$ 4,358,000	$ 4,233,000
Credit and Debit Card [Member]
Noninterest income:
Noninterest income	$ 5,925,000	$ 5,354,000	$ 4,760,000