Consolidated Statements of Income - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income
Loans, including fees	$ 137,399,000	$ 145,816,000	$ 131,763,000
Securities, taxable	7,740,000	7,919,000	6,736,000
Securities, tax-exempt	2,298,000	2,231,000	2,239,000
Other interest-earning assets	876,000	2,371,000	1,243,000
Total interest income	148,313,000	158,337,000	141,981,000
Interest expense
Deposits	14,984,000	21,264,000	13,869,000
Short-term borrowings	173,000	295,000	273,000
Federal Home Loan Bank advances	8,571,000	8,977,000	4,647,000
Subordinated debentures and other borrowings	2,339,000	3,267,000	3,110,000
Total interest expense	26,067,000	33,803,000	21,899,000
Net interest income	122,246,000	124,534,000	120,082,000
Provision for loan losses	14,050,000	1,750,000	1,100,000
Net interest income after provision for loan losses	108,196,000	122,784,000	118,982,000
Noninterest income:
Mortgage banking activities	29,346,000	8,485,000	4,109,000
Payroll processing	1,745,000	1,626,000	1,462,000
Earnings on bank owned life insurance	1,214,000	3,886,000	1,287,000
Interest rate swap program fees	932,000	0	0
Letter of credit fees	268,000	278,000	245,000
Other income	1,116,000	2,172,000	2,195,000
Total noninterest income	45,172,000	26,956,000	19,010,000
Noninterest expense
Salaries and benefits	59,799,000	53,833,000	50,910,000
Occupancy	7,950,000	7,061,000	6,711,000
Furniture and equipment rent, depreciation and maintenance	3,350,000	2,583,000	2,470,000
Data processing	10,440,000	9,235,000	8,557,000
Advertising	1,292,000	1,446,000	1,648,000
FDIC insurance costs	1,138,000	225,000	930,000
Other expense	14,551,000	14,897,000	14,944,000
Total noninterest expenses	98,520,000	89,280,000	86,170,000
Income before federal income tax expense	54,848,000	60,460,000	51,822,000
Federal income tax expense	10,710,000	11,004,000	9,798,000
Net income	$ 44,138,000	$ 49,456,000	$ 42,024,000
Earnings per common share:
Basic (in dollars per share)	$ 2.71	$ 3.01	$ 2.53
Diluted (in dollars per share)	$ 2.71	$ 3.01	$ 2.53
Deposit Account [Member]
Noninterest income:
Service charges on deposit and sweep accounts	$ 4,578,000	$ 4,584,000	$ 4,358,000
Credit and Debit Card [Member]
Noninterest income:
Service charges on deposit and sweep accounts	$ 5,973,000	$ 5,925,000	$ 5,354,000