Consolidated Statements of Cash Flows	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Cash flow from operating activities
Net income	$ 87,204,000	$ 76,648,000	$ 64,960,000
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	15,681,000	14,354,000	12,307,000
Provision for loan losses	2,950,000	6,075,000	1,500,000
Deferred income tax expense (benefit)	9,211,000	(5,000)	10,220,000
Tax Expense related to a change in tax law	466,000	0	0
Loss on write-down of investments in securities available for sale	(3,000)	26,000	405,000
Net (gain) loss on bank premises and equipment	(108,000)	114,000	221,000
Loss on extinguishment of debt	0	437,000	122,000
Net loss on other real estate owned and foreclosed assets	288,000	29,000	1,152,000
Realized gain on sale leaseback transaction	(1,034,000)	(1,034,000)	(1,034,000)
Stock based compensation	3,333,000	2,965,000	2,490,000
Excess tax benefit related to equity award activity	0	(476,000)	(1,042,000)
Increase in cash surrender value of life insurance policies	(4,127,000)	(4,089,000)	(3,692,000)
Change in Fair Value on Loans Held for Sale	113,000	(87,000)	22,000
Net change in:
Trading assets	(520,000)	(448,000)	(356,000)
Loans held for sale	1,258,000	(62,000)	876,000
Other assets	20,022,000	7,627,000	3,842,000
Other liabilities	(3,825,000)	(8,738,000)	(2,450,000)
Total adjustments	43,705,000	16,688,000	24,583,000
Net cash provided by operating activities	130,909,000	93,336,000	89,543,000
Cash flows used in investing activities
Proceeds from sales of securities available for sale	1,027,000	618,000	14,199,000
Proceeds from maturities and principal repayments of securities available for sale	54,191,000	69,775,000	78,497,000
Purchases of securities available for sale	(140,885,000)	(69,671,000)	(73,064,000)
Proceeds from maturities and principal repayments of securities held to maturity	78,757,000	90,991,000	60,168,000
Purchases of securities held to maturity	(89,033,000)	(100,198,000)	(162,021,000)
Net redemption of Federal Home Loan Bank stock	386,000	5,229,000	23,054,000
Investments in low income housing projects	(7,645,000)	(7,626,000)	(15,055,000)
Purchases of life insurance policies	(164,000)	(163,000)	(162,000)
Net increase in loans	(204,702,000)	(227,838,000)	(114,550,000)
Cash Acquired in Excess of Payments to Acquire Business	6,289,000	8,668,000
Net cash acquired (used) in business combinations			(13,448,000)
Purchases of bank premises and equipment	(25,080,000)	(10,395,000)	(10,488,000)
Proceeds from the sale of bank premises and equipment	6,306,000	345,000	1,233,000
Proceeds from the sale of other real estate owned and foreclosed assets	3,784,000	1,583,000	7,667,000
Net payments relating to other real estate owned and foreclosed assets	0	(204,000)	(1,571,000)
Net cash used in investing activities	(316,769,000)	(238,886,000)	(205,541,000)
Cash flows provided by financing activities
Net decrease in time deposits	(19,509,000)	(104,803,000)	(80,726,000)
Net increase in other deposits	177,241,000	350,739,000	428,713,000
Net repayments of short-term Federal Home Loan Bank borrowings	0	(37,000,000)	(10,000,000)
Repayments of long-term Federal Home Loan Bank borrowings	0	(65,791,000)	(9,000,000)
Net increase (decrease) in customer repurchase agreements	(14,234,000)	42,955,000	(13,932,000)
Increase (Decrease) in Payables under Repurchase Agreements	0	0	(50,000,000)
Repayments of Subordinated Debt	0	0	(30,000,000)
Net proceeds from exercise of stock options	214,000	201,000	1,367,000
Restricted stock awards issued, net of awards surrendered	(1,422,000)	(696,000)	(657,000)
Excess tax benefit from stock based compensation		476,000	1,042,000
Tax benefit from deferred compensation distribution		187,000	179,000
Proceeds from shares issued under the direct stock purchase plan	1,636,000	2,323,000	2,695,000
Common dividends paid	(34,045,000)	(29,711,000)	(26,172,000)
Net cash provided by financing activities	109,881,000	158,880,000	213,509,000
Net increase (decrease) in cash and cash equivalents	(75,979,000)	13,330,000	97,511,000
Cash and cash equivalents at beginning of year	289,095,000	275,765,000	178,254,000
Cash and cash equivalents at end of period	213,116,000	289,095,000	275,765,000
Supplemental schedule of noncash investing and financing activities
Interest on deposits and borrowings	18,626,000	18,963,000	20,773,000
Income taxes	32,865,000	33,473,000	11,841,000
Transfer of loans to other real estate owned and foreclosed assets	511,000	1,322,000	1,522,000
Real Estate Owned, Transfer to Real Estate Owned			142,000
Capital commitment relating to Low Income Housing Project investments, noncash	20,000	5,180,000	1,658,000
In conjunction with the Company's acquisitions, assets were acquired and liabilities were assumed as follows
Common stock issued for acquisition	23,468,000	40,730,000	86,415,000
Fair value of assets acquired, net of cash acquired	179,252,000	266,242,000	598,376,000
Fair value of liabilities assumed	$ 162,073,000	$ 234,180,000	$ 498,513,000