CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest incomeand divided income:
Loans	$ 631,047	$ 602,998	$ 553,647
Investment securities	58,547	59,546	60,224
Money martket investments and interest-bearing cash accounts	3,388	13,353	11,096
Total interest income	692,982	675,897	624,967
Interest expense:
Deposits	68,388	77,782	67,651
Loans payable	21	0	0
Securities sold under agreements to repurchase	6,645	6,647	9,401
Advances from FHLB	11,251	14,963	13,549
Other borrowings	6,355	9,424	8,983
Total interest expense	92,660	108,816	99,584
Net interest income	600,322	567,081	525,383
Provision for Loan, Lease, and Other Losses [Abstract]
Provision for Loan and Lease Losses	168,717	40,225	59,253
Provision for credit losses	170,985	39,813	58,989
Net interest income after provision for loan and lease losses	429,337	527,268	466,394
Non-interest income:
Service charges and fees on deposits accounts	24,612	23,916	21,679
Mortgage banking activities	22,124	17,058	17,228
Net gain (loss) on sale of investments	13,198	(497)	(84)
Gain on early extinguishment of debt	94	0	2,316
Insurance commission income	9,364	10,186	8,429
Other non-interest income	41,834	39,909	32,742
Total non-interest income	111,226	90,572	82,310
Non-interest expenses:
Employees' compensation and benefits	177,073	162,374	159,494
Occupancy and equipment	74,633	63,169	57,942
Business promotion	12,145	15,710	14,808
Professional fees	52,633	45,889	43,497
Taxes, other than income taxes	17,762	15,325	14,707
FDIC deposit insurance	6,488	6,319	8,909
Net loss on other real estate owned (OREO) and OREO operations	3,598	14,644	14,452
Credit and debit card processing expenses	19,144	16,472	15,546
Communications	8,437	6,891	6,372
Merger and restructuring costs	26,509	11,442	0
Other non-interest expenses	25,818	20,233	22,339
Total non-interest expenses	424,240	378,468	358,066
Income before income taxes	116,323	239,372	190,638
Income tax expense (benefit)	14,050	71,995	(10,970)
Net income	102,273	167,377	201,608
Net income attributable to common stockholders	$ 99,597	$ 164,701	$ 198,932
Net income per common share:
Basic	$ 0.46	$ 0.76	$ 0.92
Diluted	$ 0.46	$ 0.76	$ 0.92
Debt Securities [Member]
Provision for Loan, Lease, and Other Losses [Abstract]
Provision for Other Credit Losses	$ 1,085	$ 0	$ 0
Unfunded Loan Commitment [Member]
Provision for Loan, Lease, and Other Losses [Abstract]
Provision for Other Credit Losses	$ 1,183	$ (412)	$ (264)