Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income	$ 82,151	$ 78,409	$ 76,425
Adjustments to reconcile net income to net cash provided by operating activities
Provision for loan losses	30,988	25,431	18,285
Depreciation and amortization of premises and equipment	9,056	9,023	8,646
Net accretion on securities	4,786	5,278	2,554
Amortization of intangible assets	3,960	3,928	4,864
Excess tax benefit on stock-based compensation	1,769	1,055	(43)
Stock-based compensation expense	3,644	4,378	4,086
Bank owned life insurance income	(5,175)	(5,195)	(4,334)
Trading security purchases	(1,586)	(287)	(810)
Net unrealized (gains) losses in trading securities	(623)	(594)	226
Proceeds from sales of loans held for sale	111,284	96,603	72,498
Originations and purchases of loans held for sale	(111,206)	(96,692)	(69,677)
Net gains on sales of loans held for sale	(349)	(499)	(239)
Net security (gains) losses	(1,867)	644	(3,087)
Net (gains) on sales and write-down of other real estate owned	(221)	(687)	(1,337)
(Gain) on sale of equity investment	(818)	0	(4,179)
Impairment write-down of equity security	1,312	0	0
Impairment write-down of goodwill and intangible assets	1,530	2,565	0
(Gain) on asset sold	0	(2,462)	0
Re-evaluation of deferred tax amounts from Tax Act	4,407	0	0
Net decrease in other assets	28	364	15,386
Net increase (decrease) in other liabilities	3,834	(10,697)	5,236
Net cash provided by operating activities	136,904	110,565	124,500
Investing activities
Net cash (used in) acquisitions	(4,000)	(2,000)	(3,100)
Securities available for sale:
Proceeds from maturities, calls and principal paydowns	290,613	324,781	299,302
Proceeds from sales	14,788	98,466	15,091
Purchases	(233,804)	(597,428)	(481,262)
Securities held to maturity:
Proceeds from maturities, calls, and principal paydowns	103,759	100,893	79,212
Proceeds from sales	764	0	0
Purchases	(60,706)	(157,418)	(95,272)
Other:
Net increase in loans	(419,114)	(344,448)	(315,363)
Proceeds from Federal Home Loan Bank stock redemption	248,887	158,818	60,852
Purchases of Federal Reserve Bank and Federal Home Loan Bank stock	(248,560)	(169,178)	(64,899)
Proceeds from settlement of bank owned life insurance	799	1,477	1,541
Purchase of bank owned life insurance	0	(47,250)	0
Purchases of premises and equipment, net	(6,691)	(3,308)	(8,193)
Proceeds from sale of equity investment	818	0	4,179
Proceeds from sales of other real estate owned	7,254	6,635	3,908
Net cash provided by (used in) investing activities	(305,193)	(629,960)	(504,004)
Financing activities
Net increase in deposits	196,948	368,845	305,238
Net increase in short-term borrowings	37,419	239,222	125,679
Proceeds from issuance of long-term debt	25,000	23,880	0
Repayments of long-term debt	(40,218)	(50,240)	(498)
Proceeds from the issuance of shares to employee benefit plans and other stock plans	3,309	6,032	9,356
Cash paid by employer for tax-withholding on stock issuance	(3,582)	(3,387)	(1,664)
Purchase of treasury stock	0	(17,193)	(26,797)
Cash dividends	(40,104)	(38,880)	(38,149)
Net cash provided by (used in) financing activities	178,772	528,279	373,165
Net increase (decrease) in cash and cash equivalents	10,483	8,884	(6,339)
Cash and cash equivalents at beginning of year	149,181	140,297	146,636
Cash and cash equivalents at end of year	159,664	149,181	140,297
Cash paid during the year for:
Interest expense	25,887	22,466	20,908
Income taxes paid, net of refund	33,675	40,879	28,684
Noncash investing activities:
Loans transferred to other real estate owned	5,981	6,863	3,293
Acquisitions:
Fair value of assets acquired	$ 3,096	$ 2,584	$ 1,756