CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities:
Net income	$ 164,676	$ 169,063	$ 168,641
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation	15,963	15,891	15,749
Amortization of intangible assets	14,297	15,956	18,155
Net accretion on securities, loans and borrowings	(11,353)	(6,176)	(9,404)
Stock-based compensation	6,419	5,285	6,064
Provision for credit losses	14,212	8,430	10,837
(Benefit)/provision for deferred income taxes	(2,336)	(2,302)	2,663
Amortization of mortgage servicing rights	379	378	449
Unrealized loss/(gain) on equity securities	6	(19)	(657)
(Gain)/loss on debt extinguishment	(421)	0	318
Income from bank-owned life insurance policies	(1,915)	(1,678)	(1,579)
Gain on sales of investment securities, net	0	(4,882)	0
Net (gain)/loss on sale of loans and other assets	(3,505)	11	(80)
Change in other assets and liabilities	(16,939)	2,545	10,252
Net cash provided by operating activities	179,483	202,502	221,408
Investing activities:
Proceeds from sales of available-for-sale investment securities	0	590,179	0
Proceeds from maturities, calls and paydowns of available-for-sale investment securities	885,549	209,857	140,784
Proceeds from maturities and redemptions of equity and other securities	516	3,995	5,867
Purchases of available-for-sale investment securities	(1,114,914)	(810,122)	(78,131)
Purchases of equity and other securities	(3,234)	(202)	(31)
Net (increase) decrease in loans	(185,131)	(140,382)	(35,414)
Cash received /(paid) for acquisition, net of cash acquired of $55,973, $90,381, and $16, respectively	34,360	(4,653)	(1,737)
Settlement of bank owned life insurance policies	0	1,597	0
Purchases of premises and equipment, net	(14,395)	(5,686)	(12,646)
Real estate limited partnership investments	(1,471)	(1,637)	(1,197)
Net cash (used in)/provided by investing activities	(398,720)	(157,054)	17,495
Financing activities:
Net increase (decrease) in deposits	1,713,733	104,435	(122,049)
Net increase/(decrease) in borrowings, net of payments of $3,092, $646, and $95	30,908	(64,405)	(47,339)
Payments on subordinated debt held by unconsolidated subsidiary trusts	(2,062)	(22,681)	(25,207)
Payments on subordinated notes payable	(10,000)	0	0
Issuance of common stock	15,792	6,915	6,443
Purchase of treasury stock	(271)	(286)	(298)
Sale of treasury stock	85	6,884	12,561
Increase in deferred compensation agreements	271	286	298
Cash dividends paid	(87,131)	(80,241)	(71,495)
Withholding taxes paid on share-based compensation	(1,313)	(3,159)	(1,021)
Net cash provided by/(used in) financing activities	1,660,012	(52,252)	(248,107)
Change in cash and cash equivalents	1,440,775	(6,804)	(9,204)
Cash and cash equivalents at beginning of year	205,030	211,834	221,038
Cash and cash equivalents at end of year	1,645,805	205,030	211,834
Supplemental disclosures of cash flow information:
Cash paid for interest	21,169	25,425	17,926
Cash paid for income taxes	39,578	46,457	30,266
Supplemental disclosures of noncash financing activities
Dividends declared and unpaid	22,695	21,342	19,808
Transfers from loans to other real estate	1,291	2,522	3,299
Acquisitions:
Common stock issued	76,942	0	0
Fair value of assets acquired, excluding acquired cash and intangibles	547,654	548,856	115
Fair value of liabilities assumed	$ 529,431	$ 589,733	$ 31