CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
OPERATING ACTIVITIES
Net income	$ 82,153	$ 74,554	$ 74,138
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and net amortization	12,084	12,111	14,045
Securities premium amortization (discount accretion), net	24,291	13,874	13,675
Loan (discount accretion) premium amortization, net	(1,107)	(1,211)	(2,333)
Provision for credit losses	20,201	5,101	8,437
Stock compensation expense	3,020	2,388	2,317
Deferred tax (benefit) expense	(4,430)	122	6,154
Net (gain) loss on sale of AFS securities	(8,257)	(756)	1,839
Net loss on premises and equipment	877	592	768
Gross proceeds from sales of loans held for sale	74,814	22,041	24,092
Gross originations of loans held for sale	(78,126)	(21,823)	(22,692)
Net loss (gain) on OREO	151	(100)	433
Retirement plan curtailment expense	163	0	0
Retirement plan settlement expense	215	0	0
Net gain on sale of customer receivables	0	0	(124)
Net change in:
Interest receivable	(10,256)	(1,165)	1,204
Other assets	(6,445)	(12,275)	(2,166)
Interest payable	(3,234)	530	1,257
Other liabilities	(15,594)	(13,377)	1,358
Net cash provided by operating activities	90,520	80,606	122,402
Securities AFS:
Purchases	(916,873)	(1,253,139)	(306,867)
Sales	316,043	751,116	428,518
Maturities, calls and principal repayments	437,098	201,529	137,883
Securities HTM:
Maturities, calls and principal repayments	26,044	27,833	3,064
Proceeds from redemption of FHLB stock and equity investments	31,000	8,788	24,360
Purchases of FHLB stock and equity investments	(5,689)	(26,483)	(1,518)
Net loan originations	(90,206)	(262,137)	(24,491)
Proceeds from sales of customer receivables	0	0	4,300
Purchases of premises and equipment	(11,435)	(15,883)	(13,444)
(Purchases for) proceeds of BOLI	(12,500)	0	5,956
Proceeds from sales of premises and equipment	1,846	96	1,943
Proceeds from sales of OREO	766	1,122	1,717
Proceeds from sales of repossessed assets	171	328	483
Net cash (used in) provided by investing activities	(223,735)	(566,830)	261,904
FINANCING ACTIVITIES:
Net change in deposits	249,321	272,638	(106,014)
Net change in other borrowings	(5,186)	(8,452)	27,312
Proceeds from FHLB	21,797,280	6,914,800	4,201,500
Repayment of FHLB	(21,937,497)	(6,661,119)	(4,499,788)
Net proceeds from issuance of subordinated long-term debt	98,478	0	0
Proceeds from stock option exercises	1,692	1,986	2,653
Cash paid to tax authority related to tax withholding on share-based awards	(393)	(394)	(248)
Purchase of common stock	(30,989)	(2,181)	(47,193)
Proceeds from the issuance of common stock for dividend reinvestment plan	1,424	1,445	1,478
Cash dividends paid	(43,204)	(42,521)	(41,979)
Net cash provided by (used in) financing activities	130,926	476,202	(462,279)
Net (decrease) increase in cash and cash equivalents	(2,289)	(10,022)	(77,973)
Cash and cash equivalents at beginning of period	110,697	120,719	198,692
Cash and cash equivalents at end of period	108,408	110,697	120,719
SUPPLEMENTAL DISCLOSURES FOR CASH FLOW INFORMATION:
Interest paid	47,201	70,452	55,844
Income taxes paid	12,000	10,500	2,000
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Loans transferred to other repossessed assets and real estate through foreclosure	749	649	2,128
Loans transferred from portfolio to held for sale	0	0	3,984
Transfer of HTM securities to AFS securities	0	0	743,421
Unsettled trades to purchase securities	0	(17,538)	(6,378)
Unsettled issuances of brokered CDs	$ 0	$ 20,000	$ 15,236