Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income:
Interest and fees on loans, including loans held for sale		$ 160,826	$ 164,991	$ 154,552
Interest and dividends on securities:
Taxable		11,939	12,516	10,015
Tax exempt		2,380	2,354	2,796
Interest and dividends on Federal Reserve Bank and Federal Home Loan Bank stock		532	947	1,303
Interest on Federal Reserve Bank deposits		704	4,434	2,525
Other, including interest on federal funds sold		60	156	259
Total interest income		176,441	185,398	171,450
Interest expense:
Interest on deposits		21,177	33,371	23,714
Interest on repurchase agreements and federal funds purchased		2,788	4,631	3,312
Interest on advances from Federal Home Loan Bank		0	39	27
Interest on long-term debt		1,485	2,472	2,242
Total interest expense		25,450	40,513	29,295
Net interest income		150,991	144,885	142,155
Provision for credit losses	[1]	16,047	4,819	6,167
Net interest income after provision for credit losses		134,944	140,066	135,988
Noninterest income:
Service charges on deposit accounts		23,461	26,359	25,974
Gains on sales of loans, net		7,226	1,880	1,288
Trust and wealth management income		10,931	10,804	11,313
Loan related fees		4,041	2,742	3,729
Bank owned life insurance		2,306	2,397	3,672
Brokerage revenue		1,483	1,367	1,354
Securities gains (losses)		1,769	783	(85)
Other noninterest income		3,343	3,852	4,707
Total noninterest income		54,560	50,184	51,952
Noninterest expense:
Officer salaries and employee benefits		15,257	12,614	12,906
Other salaries and employee benefits		51,170	50,413	48,656
Occupancy, net		7,912	7,845	8,167
Equipment		2,737	3,000	2,878
Data processing		7,941	7,417	6,680
Bank franchise tax		7,299	6,771	6,557
Legal fees		1,634	1,968	1,637
Professional fees		2,091	2,188	2,093
Advertising and marketing		2,980	3,283	2,995
FDIC insurance		1,056	266	1,171
Other real estate owned provision and expense		2,655	5,490	4,324
Repossession expense		717	1,042	1,249
Amortization of limited partnership investments		3,759	3,422	2,527
Other noninterest expense		12,031	12,539	15,558
Total noninterest expense		119,239	118,258	117,398
Income before income taxes		70,265	71,992	70,542
Income taxes		10,761	7,452	11,314
Net income		59,504	64,540	59,228
Unrealized holding gains (losses) on debt securities available-for-sale:
Unrealized holding gains (losses) arising during the period		13,839	14,270	(5,393)
Less: Reclassification adjustments for realized gains (losses) included in net income		1,251	3	(821)
Tax expense (benefit)		3,273	3,403	(960)
Other comprehensive income (loss), net of tax		9,315	10,864	(3,612)
Comprehensive income		$ 68,819	$ 75,404	$ 55,616
Basic earnings per share (in dollars per share)		$ 3.35	$ 3.64	$ 3.35
Diluted earnings per share (in dollars per share)		$ 3.35	$ 3.64	$ 3.35
Weighted average shares outstanding-basic (in shares)		17,748	17,724	17,687
Weighted average shares outstanding-diluted (in shares)		17,756	17,740	17,703

[1] Effective January 1, 2020, the provision for loan losses became the provision for credit losses with the implementation of ASU 2016-13, commonly referred to as CECL.