Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net income	$ 112,566	$ 82,151	$ 78,409
Adjustments to reconcile net income to net cash provided by operating activities
Provision for loan losses	28,828	30,988	25,431
Depreciation and amortization of premises and equipment	9,280	9,056	9,023
Net amortization on securities	4,007	4,786	5,278
Amortization of intangible assets	4,042	3,960	3,928
Excess tax (benefit) on stock-based compensation	(543)	(1,769)	(1,055)
Stock-based compensation expense	3,936	3,644	4,378
Bank owned life insurance income	(5,091)	(5,175)	(5,195)
Trading security purchases	0	(1,586)	(287)
Net unrealized losses on trading securities	0	(623)	(594)
Proceeds from sales of loans held for sale	102,547	111,284	96,603
Originations and purchases of loans held for sale	(108,070)	(111,206)	(96,692)
Net gains on sales of loans held for sale	(286)	(349)	(499)
Net security losses (gains)	6,341	(1,867)	644
Net gains on sales and write-down of other real estate owned	(230)	(221)	(687)
Gain on sale of equity investment	0	(818)	0
Impairment write-down of equity security	0	1,312	0
Impairment write-down of goodwill and intangible assets	0	1,530	2,565
Gain on asset sold	0	0	(2,462)
Re-evaluation of deferred tax amounts from Tax Act	0	4,407	0
Net change in other assets and other liabilities	(9,554)	7,400	(8,223)
Net cash provided by operating activities	147,773	136,904	110,565
Investing activities
Net cash used in acquisitions	(7,884)	(4,000)	(2,000)
Securities available for sale:
Proceeds from maturities, calls and principal paydowns	259,446	290,613	324,781
Proceeds from sales	101,315	14,788	98,466
Purchases	(132,448)	(233,804)	(597,428)
Securities held to maturity:
Proceeds from maturities, calls and principal paydowns	100,738	103,759	100,893
Proceeds from sales	0	764	0
Purchases	(400,602)	(60,706)	(157,418)
Equity securities:
Proceeds from sales	3,318	0	0
Purchases	(2)	0	0
Other:
Net increase in loans	(331,166)	(419,114)	(344,448)
Proceeds from Federal Home Loan Bank stock redemption	246,844	248,887	158,818
Purchases of Federal Home Loan Bank stock	(253,367)	(248,560)	(169,178)
Proceeds from settlement of bank owned life insurance	0	799	1,477
Purchase of bank owned life insurance	0	0	(47,250)
Purchases of premises and equipment, net	(7,402)	(6,691)	(3,308)
Proceeds from sale of equity investment	0	818	0
Proceeds from the sales of other real estate owned	3,591	7,254	6,635
Net cash provided by (used in) investing activities	(417,619)	(305,193)	(629,960)
Financing activities
Net increase in deposits	197,575	196,948	368,845
Net increase in short-term borrowings	152,573	37,419	239,222
Proceeds from issuance of long-term debt	25,000	25,000	23,880
Repayments of long-term debt	(40,145)	(40,218)	(50,240)
Proceeds from the issuance of shares to employee and other stock plans	1,296	3,309	6,032
Cash paid by employer for tax-withholdings on stock issuance	(1,893)	(3,582)	(3,387)
Purchase of treasury stock	0	0	(17,193)
Cash dividends	(43,269)	(40,104)	(38,880)
Net cash (used in) financing activities	291,137	178,772	528,279
Net (decrease) increase in cash and cash equivalents	21,291	10,483	8,884
Cash and cash equivalents at beginning of year	159,664	149,181	140,297
Cash and cash equivalents at end of year	180,955	159,664	149,181
Cash paid during the period for:
Interest expense	36,691	25,887	22,466
Income taxes paid, net of refund	31,898	33,675	40,879
Noncash investing activities:
Loans transferred to other real estate owned	1,273	5,981	6,863
Acquisitions:
Fair value of assets acquired	$ 6,274	$ 3,096	$ 2,584