Consolidated Statements of Income - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income
Loans, including fees	$ 131,763,000	$ 116,816,000	$ 109,049,000
Securities, taxable	6,736,000	5,326,000	6,842,000
Securities, tax-exempt	2,239,000	2,305,000	2,165,000
Other interest-earning assets	1,243,000	1,096,000	401,000
Total interest income	141,981,000	125,543,000	118,457,000
Interest expense
Deposits	13,869,000	9,362,000	7,549,000
Short-term borrowings	273,000	190,000	211,000
Federal Home Loan Bank advances	4,647,000	3,657,000	2,263,000
Subordinated debentures and other borrowings	3,110,000	2,586,000	2,567,000
Total interest expense	21,899,000	15,795,000	12,590,000
Net interest income	120,082,000	109,748,000	105,867,000
Provision for loan losses	1,100,000	2,950,000	2,900,000
Net interest income after provision for loan losses	118,982,000	106,798,000	102,967,000
Noninterest income:
Payroll processing	1,462,000	1,305,000	1,016,000
Earnings on bank owned life insurance	1,287,000	2,731,000	1,264,000
Letter of credit fees	245,000	348,000	493,000
Gain on trust preferred securities repurchase	0	0	2,970,000
Other income	2,195,000	1,203,000	2,898,000
Total noninterest income	19,010,000	19,001,000	21,038,000
Noninterest expense
Salaries and benefits	50,910,000	45,397,000	43,524,000
Occupancy	6,711,000	6,186,000	6,063,000
Furniture and equipment rent, depreciation and maintenance	2,470,000	2,168,000	2,119,000
Data processing	8,557,000	8,222,000	7,939,000
Advertising	1,648,000	1,608,000	1,586,000
FDIC insurance costs	930,000	960,000	1,236,000
Problem asset costs	90,000	355,000	338,000
Efficiency program-related costs	0	0	172,000
Other expense	14,854,000	14,820,000	14,141,000
Total noninterest expenses	86,170,000	79,716,000	77,118,000
Income before federal income tax expense	51,822,000	46,083,000	46,887,000
Federal income tax expense	9,798,000	14,809,000	14,974,000
Net income	$ 42,024,000	$ 31,274,000	$ 31,913,000
Earnings per common share:
Basic (in dollars per share)	$ 2.53	$ 1.90	$ 1.96
Diluted (in dollars per share)	$ 2.53	$ 1.90	$ 1.96
Deposit Account [Member]
Noninterest income:
Noninterest income	$ 4,358,000	$ 4,233,000	$ 4,253,000
Credit and Debit Card [Member]
Noninterest income:
Noninterest income	5,354,000	4,760,000	4,278,000
Mortgage Banking [Member]
Noninterest income:
Noninterest income	$ 4,109,000	$ 4,421,000	$ 3,866,000