Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 107,172	$ (111,033)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,083	7,880
Provision for credit losses	(4,911)	246,793
(Gain) loss on other real estate and foreclosed assets	(253)	10,550
Gain on sale of securities		(112)
Deferred tax expense (benefit)	2,300	(34,279)
Increase in cash surrender value of life insurance contracts	(9,400)	(646)
Net (increase) decrease in loans held for sale	8,031	(5,709)
Net amortization of securities premium/discount	13,211	9,349
Amortization of intangible assets	4,419	5,345
Stock-based compensation expense	5,517	5,583
Net change in liability from variation margin collateral	56,744	(105,921)
Decrease in interest payable and other liabilities	(23,472)	(18,641)
Decrease in other assets	98,052	9,887
Other, net	(9,453)	(7,521)
Net cash provided by operating activities	255,040	11,525
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from the sale of available for sale securities		124,122
Proceeds from maturities of securities available for sale	311,232	166,265
Purchases of securities available for sale	(1,164,798)	(367,944)
Proceeds from maturities of securities held to maturity	37,830	84,176
Purchases of securities held to maturity	(59,362)
Net increase in short-term investments	(1,005,325)	(766,085)
Proceeds from sales of loans and leases	7,373	2,608
Net (increase) decrease in loans	101,924	(339,888)
Purchase of life insurance contracts	(45,000)
Proceeds from the surrender of life insurance contracts	44,045
Purchases of property and equipment	(4,269)	(9,460)
Proceeds from sales of other real estate	4,191	3,007
Other, net	5,809	(1,731)
Net cash used in investing activities	(1,766,350)	(1,104,930)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase in deposits	1,512,643	1,204,921
Net decrease in short-term borrowings	(14,766)	(41,589)
Proceeds from the issuance of long-term debt	22,388
Repayments of long-term debt	(3,209)	(76)
Dividends paid	(24,021)	(24,028)
Payroll tax remitted on net share settlement of equity awards	(494)	(1,494)
Proceeds from exercise of stock options	132
Proceeds from dividend reinvestment and stock purchase plans	1,004	984
Settlement of forward contract portion of accelerated share repurchase		12,110
Repurchase of shares		(12,716)
Net cash provided by financing activities	1,493,677	1,138,112
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	(17,633)	44,707
CASH AND DUE FROM BANKS, BEGINNING	526,306	432,104
CASH AND DUE FROM BANKS, ENDING	508,673	476,811
SUPPLEMENTAL INFORMATION FOR NON-CASH INVESTING AND FINANCING ACTIVITIES
Assets acquired in settlement of loans	$ 1,799	$ 1,612