Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash Flows from Operating Activities
Net income	$ 56,794		$ 72,835	$ 157,967	$ 211,758
Adjustments to reconcile net income to net cash provided by operating activities:
Provision/(reversal) for credit losses	12,500	$ 25,000	(2,000)	62,500	(2,000)
Provision for losses on other real estate owned				717	494
Deferred tax (benefit)/provision				(10,305)	9,911
Depreciation and amortization				5,644	5,009
Amortization of right-of-use asset				6,624	6,248
Change in operating lease liabilities				(757)	(5,298)
Net gains on sale and transfer of other real estate owned				(4,216)	(193)
Net gains on sale of loans held for sale				(219)	(795)
Proceeds from sales of loans held for sale				6,406	38,742
Originations of loans held for sale				(6,187)	0
Amortization on alternative energy partnerships, venture capital and other investments				42,904	27,009
Net (gain)/loss on sales and calls of securities				(1,153)	108
Amortization/accretion of security premiums/discounts, net				6,211	2,376
Loss on sales or disposal of fixed assets				45	0
Unrealized loss/(gain) on equity securities	1,600		(400)	1,928	(7,764)
Stock based compensation and stock issued to officers as compensation				4,608	5,597
Net change in accrued interest receivable and other assets				(13,000)	(31,640)
Net change in other liabilities				(26,597)	64,186
Net cash provided by operating activities				233,120	323,748
Cash Flows from Investing Activities
Purchase of investment securities available-for-sale				(272,961)	(539,979)
Proceeds from sale of investment securities available-for-sale				107,539	149,725
Proceeds from sale of equity securities				3,112	0
Proceeds from repayments, maturities and calls of investment securities available-for-sale				543,114	233,058
Purchase of Federal Home Loan Bank stock				(840)	(975)
Redemptions of Federal Home Loan Bank stock				1,680	975
Net increase in loans				(496,732)	(803,291)
Purchase of premises and equipment				(4,372)	(5,125)
Proceeds from sales of other real estate owned				4,308	1,905
Net increase in investment in affordable housing and alternative energy partnerships				(60,129)	(35,952)
Net cash used for investing activities				(175,281)	(999,659)
Cash Flows from Financing Activities
Net increase in deposits				1,342,019	955,679
Advances from Federal Home Loan Bank				1,450,000	3,610,000
Repayment of Federal Home Loan Bank borrowings				(1,890,000)	(3,540,000)
Cash dividends paid				(74,014)	(74,422)
Repayment of other borrowings				(7,663)	(39,918)
Proceeds from other borrowings				0	25,507
Purchases of treasury stock				(12,880)	(36,301)
Repayment of short-term borrowings				(25,683)	0
Proceeds from shares issued under Dividend Reinvestment Plan				2,573	2,522
Taxes paid related to net share settlement of RSUs				(1,903)	(2,300)
Net cash provided by financing activities				782,449	900,767
Increase in cash, cash equivalents, and restricted cash				840,288	224,856
Cash, cash equivalents, and restricted cash, beginning of the period		$ 593,778		593,778	600,290	$ 600,290
Cash, cash equivalents, and restricted cash, end of the period	$ 1,434,066		$ 825,146	1,434,066	825,146	$ 593,778
Supplemental disclosure of cash flow information
Interest				133,151	137,422
Income taxes paid				35,490	43,507
Non-cash investing and financing activities:
Net change in unrealized holding loss on securities available-for-sale, net of tax				8,068	21,292
Net change in unrealized holding loss on cash flow hedge derivatives				(3,981)	(4,119)
Transfers to other real estate owned from loans held for investment				0	860
Loans transferred from held for investment to held for sale, net				$ 0	$ 75,285