Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash Flows from Operating Activities
Net income	$ 72,397	$ 56,794	$ 222,980	$ 157,967
Adjustments to reconcile net income to net cash provided by operating activities:
(Reversal)/provision for credit losses	3,000	12,500	(15,710)	62,500
(Reversal)/Provision for losses on other real estate owned			(8)	717
Deferred tax (benefit)/ provision			8,867	(10,305)
Depreciation and amortization			5,942	5,644
Amortization of right-of-use asset			5,972	6,624
Change in operating lease liabilities			(1,456)	(757)
Net gains on sale and transfer of other real estate owned			(120)	(4,216)
Net gains on sale of loans			(357)	(219)
Proceeds from sales of loans			5,351	6,406
Originations of loans held for sale			(4,994)	(6,187)
Amortization on alternative energy partnerships, venture capital and other investments			31,610	42,904
Net gain on sales and calls of securities			(853)	(1,153)
Amortization/accretion of security premiums/discounts, net			6,128	6,211
Loss on sales or disposal of fixed assets			55	45
Unrealized loss on equity securities	(3)	(1,600)	3,628	1,928
Stock-based compensation and stock issued to officers as compensation			4,999	4,608
Net change in accrued interest receivable and other assets			(21,607)	(13,000)
Net change in other liabilities			(12,880)	(26,597)
Net cash provided by operating activities			237,547	233,120
Cash Flows from Investing Activities
Purchase of investment securities available-for-sale			(406,750)	(272,961)
Proceeds from sale of investment securities available-for-sale			21,102	107,539
Proceeds from sale of equity securities			0	3,112
Proceeds from repayments, maturities and calls of investment securities available-for-sale			326,527	543,114
Purchase of Federal Home Loan Bank stock			0	(840)
Redemptions of Federal Home Loan Bank stock			0	1,680
Net increase in loans			(349,924)	(496,732)
Purchase of premises and equipment			(2,828)	(4,372)
Benefits received from bank owned life insurance policies			2,752	0
Proceeds from sales of other real estate owned			0	4,308
Net increase in investment in affordable housing and alternative energy partnerships			(19,039)	(60,129)
Net cash used for investing activities			(428,160)	(175,281)
Cash Flows from Financing Activities
Net increase in deposits			897,713	1,342,019
Advances from Federal Home Loan Bank			50,000	1,450,000
Repayment of Federal Home Loan Bank borrowings			(180,000)	(1,890,000)
Cash dividends paid			(73,335)	(74,014)
Repayment of other borrowings			0	(7,663)
Purchases of treasury stock			(100,668)	(12,880)
Repayment of short-term borrowings			0	(25,683)
Proceeds from shares issued under Dividend Reinvestment Plan			2,619	2,573
Taxes paid related to net share settlement of RSUs			(2,632)	(1,903)
Net cash provided by financing activities			593,697	782,449
Decrease in cash, cash equivalents, and restricted cash			403,084	840,288
Cash, cash equivalents, and restricted cash, beginning of the period			1,421,078	593,778	$ 593,778
Cash, cash equivalents, and restricted cash, end of the period	$ 1,824,162	$ 1,434,066	1,824,162	1,434,066	$ 1,421,078
Supplemental disclosure of cash flow information
Interest			61,574	133,151
Income taxes paid			65,291	35,490
Non-cash investing and financing activities:
Net change in unrealized holding (loss)/gain on securities available-for-sale, net of tax			(7,872)	8,068
Net change in unrealized holding gain/(loss) on cash flow hedge derivatives			2,194	(3,981)
Transfers to other real estate owned from loans held for investment			$ 205	$ 0