Consolidated Statements of Income - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income
Loans, including fees	$ 116,816,000	$ 109,049,000	$ 104,106,000
Securities, taxable	5,326,000	6,842,000	5,918,000
Securities, tax-exempt	2,305,000	2,165,000	2,089,000
Other interest-earning assets	1,096,000	401,000	215,000
Total interest income	125,543,000	118,457,000	112,328,000
Interest expense
Deposits	9,362,000	7,549,000	7,590,000
Short-term borrowings	190,000	211,000	157,000
Federal Home Loan Bank advances	3,657,000	2,263,000	765,000
Subordinated debentures and other borrowings	2,586,000	2,567,000	2,642,000
Total interest expense	15,795,000	12,590,000	11,154,000
Net interest income	109,748,000	105,867,000	101,174,000
Provision for loan losses	2,950,000	2,900,000	(1,000,000)
Net interest income after provision for loan losses	106,798,000	102,967,000	102,174,000
Noninterest income
Service charges on deposit and sweep accounts	4,233,000	4,253,000	3,308,000
Credit and debit card fees	4,760,000	4,278,000	4,329,000
Mortgage banking activities	4,421,000	3,866,000	3,619,000
Earnings on bank owned life insurance	2,731,000	1,264,000	1,113,000
Payroll processing	1,305,000	1,016,000	969,000
Letter of credit fees	348,000	493,000	457,000
Gain on trust preferred securities repurchase	0	2,970,000	0
Other income	1,203,000	2,898,000	2,243,000
Total noninterest income	19,001,000	21,038,000	16,038,000
Noninterest expense
Salaries and benefits	45,397,000	43,524,000	42,594,000
Occupancy	6,186,000	6,063,000	5,976,000
Furniture and equipment rent, depreciation and maintenance	2,168,000	2,119,000	2,332,000
Data processing	8,222,000	7,939,000	7,696,000
Advertising	1,608,000	1,586,000	1,363,000
FDIC insurance costs	960,000	1,236,000	1,717,000
Problem asset costs	355,000	338,000	1,212,000
Efficiency program-related costs	0	172,000	765,000
Other expense	14,820,000	14,141,000	15,726,000
Total noninterest expenses	79,716,000	77,118,000	79,381,000
Income before federal income tax expense	46,083,000	46,887,000	38,831,000
Federal income tax expense	14,809,000	14,974,000	11,811,000
Net income	$ 31,274,000	$ 31,913,000	$ 27,020,000
Earnings per common share:
Basic (in dollars per share)	$ 1.90	$ 1.96	$ 1.63
Diluted (in dollars per share)	$ 1.90	$ 1.96	$ 1.62