Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net income	$ 220,621	$ 382,723	$ 360,418
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	137,750	37,800	42,000
Deferred tax expense (benefit)	(31,236)	927	9,472
Depreciation and amortization	36,616	37,507	38,750
Amortization of earning assets and funding premium/discount, net	75,929	49,731	50,984
Stock-based compensation	12,179	12,626	11,612
Gain on sale, net of write-down, on foreclosed and repossessed assets	(1,938)	(729)	(709)
Loss (gain) on sale, net of write-down, on premises and equipment	1,105	1,340	346
Gain on the sale of investment securities, net	(8)	(29)	0
Increase in cash surrender value of life insurance policies	(14,561)	(14,612)	(14,614)
Gain from life insurance policies	(1,219)	(4,933)	(2,553)
Mortgage banking activities	(18,295)	(6,115)	(4,424)
Proceeds from sale of loans held for sale	486,341	216,239	188,025
Originations of loans held for sale	(449,803)	(240,305)	(171,883)
Net change in right-of-use lease assets	27,868	2,479	0
Net decrease (increase) in derivative contract assets net of liabilities	(118,336)	(123,752)	(4,615)
Gain on sale of banking center deposits	0	0	(4,596)
Net (increase) decrease in accrued interest receivable and other assets	25,657	(23,790)	(739)
Net (decrease) increase in accrued expenses and other liabilities	(8,121)	(23,257)	(28,066)
Net cash provided by operating activities	380,549	303,850	469,408
Investing Activities:
Purchases of available-for-sale securities	(990,904)	(549,541)	(873,108)
Proceeds from maturities and principal payments of available-for-sale securities	627,577	556,283	538,747
Proceeds from sales of available-for-sale securities	8,963	70,087	0
Purchases of held-to-maturity securities	(1,297,535)	(1,571,604)	(393,693)
Proceeds from maturities and principal payments of held-to-maturity securities	983,864	573,703	524,862
Net proceeds from (purchase of) Federal Home Loan Bank stock	71,452	240	2,280
Purchases of intercompany debt securities	(12,244)	(6,065)	(1,215)
Net increase in loans	(1,681,947)	(1,642,501)	(990,014)
Proceeds from loans not originated for sale	9,197	20,931	1,687
Proceeds from life insurance policies	1,885	12,866	4,271
Proceeds from the sale of foreclosed properties and repossessed assets	11,497	11,562	8,011
Proceeds from the sale of premises and equipment	866	0	567
Additions to premises and equipment	(21,280)	(25,717)	(32,958)
Net (increase) decrease in interest-bearing deposits	0	0	(107,361)
Net cash provided by (used for) investing activities	(2,288,609)	(2,549,756)	(1,317,924)
Financing Activities:
Net increase in deposits	4,006,319	1,465,377	979,519
Proceeds from Federal Home Loan Bank advances	3,850,000	9,200,000	8,960,000
Repayments of Federal Home Loan Bank advances	(5,665,312)	(9,078,332)	(8,810,297)
Net (decrease) increase in securities sold under agreements to repurchase and other borrowings	(45,076)	458,557	(61,395)
Issuance of long-term debt	0	300,000	0
Debt issuance costs	0	(3,642)	0
Dividends paid to common shareholders	(144,965)	(140,783)	(114,959)
Dividends paid to preferred shareholders	(7,875)	(7,875)	(7,875)
Exercise of stock options	240	619	2,173
Common stock repurchased	(76,556)	(13,003)	(12,158)
Common shares acquired related to stock compensation plan activity	(3,506)	(6,616)	(13,779)
Net cash (used for) provided by financing activities	1,913,269	2,174,302	921,229
Net (decrease) increase in cash and cash equivalents	5,209	(71,604)	72,713
Cash and cash equivalents at beginning of year	257,895	329,499	256,786
Cash and cash equivalents at end of year	263,104	257,895	329,499
Supplemental disclosure of cash flow information:
Interest paid	118,123	197,200	144,726
Income taxes paid	94,072	110,057	60,925
Noncash investing and financing activities:
Transfer of loans and leases to foreclosed properties and repossessed assets	5,394	10,440	8,105
Transfer of loans from portfolio to loans held for sale	8,578	16,609	5,443
Deposits assumed	$ 4,657	$ 0	$ 0