CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net income	$ 87,047,000	$ 80,411,000	$ 57,330,000
Adjustments to reconcile net income to net cash from operating activities:
Depreciation	5,930,000	5,654,000	5,119,000
Provision for loan losses	3,235,000	6,400,000	3,000,000
Net loss on sale and write down of other real estate owned	0	16,000	12,000
Amortization of loan servicing rights	528,000	503,000	599,000
Loans originated for sale	(66,008,000)	(49,816,000)	(54,188,000)
Net gain on sales of loans	(2,043,000)	(1,713,000)	(1,749,000)
Proceeds from sale of loans	64,820,000	51,715,000	57,621,000
Net (gain) loss on sale of premises and equipment	(3,000)	1,000	79,000
Net (gain) loss on sales and calls of securities available-for-sale	(142,000)	50,000	(32,000)
Net amortization of available-for-sale securities	3,947,000	3,177,000	3,114,000
Stock based compensation expense	4,187,000	5,608,000	5,698,000
Earnings on life insurance	(1,890,000)	(1,244,000)	(1,768,000)
Gain on life insurance	(841,000)	(206,000)	0
Tax benefit of stock award issuances	(529,000)	(761,000)	(964,000)
Net change:
Interest receivable and other assets	(4,733,000)	(3,301,000)	787,000
Interest payable and other liabilities	6,534,000	8,481,000	2,584,000
Total adjustments	12,992,000	24,564,000	19,912,000
Net cash from operating activities	100,039,000	104,975,000	77,242,000
Cash flows from investing activities:
Proceeds from sale of securities available-for-sale	57,114,000	15,302,000	40,877,000
Proceeds from maturities, calls and principal paydowns of securities available-for-sale	67,818,000	53,817,000	61,745,000
Purchases of securities available-for-sale	(129,453,000)	(126,551,000)	(139,252,000)
Purchase of life insurance	(5,552,000)	(423,000)	(580,000)
Net increase in total loans	(152,119,000)	(101,670,000)	(347,217,000)
Proceeds from sales of land, premises and equipment	14,000	461,000	10,000
Purchases of land, premises and equipment	(7,998,000)	(7,968,000)	(9,582,000)
Purchase of Federal Home Loan Bank Stock	0	0	(2,250,000)
Proceeds from sales of other real estate owned	0	21,000	199,000
Proceeds from life insurance	1,483,000	569,000	0
Net cash from investing activities	(168,693,000)	(166,442,000)	(396,050,000)
Cash flows from financing activities:
Net increase in total deposits	89,754,000	35,410,000	430,743,000
Net increase (decrease) in short-term borrowings	(75,555,000)	174,903,000	20,607,000
Proceeds from short-term FHLB borrowings	0	0	80,000,000
Payments on short term FHLB borrowings	0	(80,000,000)	(180,000,000)
Payments on long-term FHLB borrowings	0	(30,000)	(2,000)
Payments on subordinated debentures	(30,928,000)	0	0
Common dividends paid	(29,639,000)	(25,278,000)	(21,396,000)
Preferred dividends paid	(13,000)	(13,000)	(13,000)
Payments related to equity incentive plan	(2,109,000)	(2,435,000)	(1,736,000)
Purchase of treasury stock	(515,000)	(463,000)	(495,000)
Sales of treasury stock	118,000	115,000	0
Net cash from financing activities	(48,887,000)	102,209,000	327,708,000
Net change in cash and cash equivalents	(117,541,000)	40,742,000	8,900,000
Cash and cash equivalents at beginning of the year	216,922,000	176,180,000	167,280,000
Cash and cash equivalents at end of the year	99,381,000	216,922,000	176,180,000
Cash paid during the year for:
Interest	58,964,000	43,606,000	29,171,000
Income taxes	21,035,000	19,033,000	29,120,000
Supplemental non-cash disclosures:
Loans transferred to other real estate owned	0	316,000	88,000
Property transferred to held for sale	0	221,000	0
Right-of-use assets obtained in exchange for lease liabilities	$ 5,483,000	$ 0	$ 0