Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income	$ 382,723,000	$ 360,418,000	$ 255,439,000
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	37,800,000	42,000,000	40,900,000
Deferred tax expense (benefit)	927,000	9,472,000	(9,074,000)
Depreciation and amortization	37,507,000	38,750,000	37,172,000
Amortization of earning assets and funding premium/discount, net	49,731,000	50,984,000	45,444,000
Stock-based compensation	12,626,000	11,612,000	12,276,000
Gain on sale, net of write-down, on foreclosed and repossessed assets	(729,000)	(709,000)	(784,000)
Loss (gain) on sale, net of write-down, on premises and equipment	1,340,000	346,000	(15,000)
Impairment loss on securities recognized in earnings	0	0	126,000
Gain on the sale of investment securities, net	29,000	0	0
Increase in cash surrender value of life insurance policies	(14,612,000)	(14,614,000)	(14,627,000)
Gain from life insurance policies	(4,933,000)	(2,553,000)	0
Mortgage banking activities	(6,115,000)	(4,424,000)	(9,937,000)
Proceeds from sale of loans held for sale	216,239,000	188,025,000	333,027,000
Originations of loans held for sale	(240,305,000)	(171,883,000)	(287,634,000)
Net change in right-of-use lease assets	2,479,000	0	0
Net decrease (increase) in derivative contract assets net of liabilities	(123,752,000)	(4,615,000)	32,763,000
Gain on sale of banking center deposits	0	(4,596,000)	0
Net (increase) decrease in accrued interest receivable and other assets	(23,790,000)	(739,000)	(19,790,000)
Net (decrease) increase in accrued expenses and other liabilities	(23,257,000)	(28,066,000)	29,680,000
Net cash provided by operating activities	303,850,000	469,408,000	444,966,000
Investing Activities:
Purchases of available-for-sale securities	(549,541,000)	(873,108,000)	(660,106,000)
Proceeds from maturities and principal payments of available-for-sale securities	556,283,000	538,747,000	984,732,000
Proceeds from sales of available-for-sale securities	70,087,000	0	0
Purchases of held-to-maturity securities	(1,571,604,000)	(393,693,000)	(1,043,278,000)
Proceeds from maturities and principal payments of held-to-maturity securities	573,703,000	524,862,000	687,439,000
Net proceeds from (purchase of) Federal Home Loan Bank stock	240,000	2,280,000	43,080,000
Purchases of intercompany debt securities	(6,065,000)	(1,215,000)	873,000
Net increase in loans	(1,642,501,000)	(990,014,000)	(549,213,000)
Proceeds from loans not originated for sale	20,931,000	1,687,000	14,679,000
Proceeds from life insurance policies	12,866,000	4,271,000	746,000
Proceeds from the sale of foreclosed properties and repossessed assets	11,562,000	8,011,000	7,603,000
Proceeds from the sale of premises and equipment	0	567,000	3,357,000
Additions to premises and equipment	(25,717,000)	(32,958,000)	(28,546,000)
Net (increase) decrease in interest-bearing deposits	0	(107,361,000)	0
Proceeds from redemption of other assets	0	0	7,581,000
Net cash provided by (used for) investing activities	(2,549,756,000)	(1,317,924,000)	(531,053,000)
Financing Activities:
Net increase in deposits	1,465,377,000	979,519,000	1,690,197,000
Proceeds from Federal Home Loan Bank advances	9,200,000,000	8,960,000,000	12,255,000,000
Repayments of Federal Home Loan Bank advances	(9,078,332,000)	(8,810,297,000)	(13,420,791,000)
Net increase (decrease) in securities sold under agreements to repurchase and other borrowings	458,557,000	(61,395,000)	(306,257,000)
Issuance of long-term debt	300,000,000	0	0
Debt issuance costs	(3,642,000)	0	0
Redemption of Series E preferred stock	0	0	(122,710,000)
Issuance of Series F preferred stock	0	0	145,056,000
Dividends paid to common shareholders	(140,783,000)	(114,959,000)	(94,630,000)
Dividends paid to preferred shareholders	(7,875,000)	(7,875,000)	(8,096,000)
Exercise of stock options	619,000	2,173,000	8,259,000
Common stock repurchased	(13,003,000)	(12,158,000)	(11,585,000)
Common shares acquired related to stock compensation plan activity	(6,616,000)	(13,779,000)	(11,694,000)
Net cash (used for) provided by financing activities	2,174,302,000	921,229,000	122,749,000
Net (decrease) increase in cash and cash equivalents	(71,604,000)	72,713,000	36,662,000
Cash and due from banks at beginning of year	329,499,000	256,786,000	220,124,000
Cash and due from banks at end of year	257,895,000	329,499,000	256,786,000
Supplemental disclosure of cash flow information:
Interest paid	197,200,000	144,726,000	114,046,000
Income taxes paid	110,057,000	60,925,000	109,059,000
Noncash investing and financing activities:
Transfer of loans and leases to foreclosed properties and repossessed assets	10,440,000	8,105,000	8,972,000
Transfer of loans from portfolio to loans held for sale	$ 16,609,000	$ 5,443,000	$ 7,234,000