Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Cash Flows from Operating Activities
Net income	$ 77,199	$ 54,321	$ 150,583	$ 101,173
Adjustments to reconcile net income to net cash provided by operating activities:
(Reversal)/provision for credit losses	(6,600)	25,000	(18,710)	50,000
Provision for losses on other real estate owned			47	717
Deferred tax provision			11,685	(4,896)
Depreciation and amortization			4,156	3,688
Amortization of right-of-use asset			4,461	4,249
Change in operating lease liabilities			710	535
Net gains on sale and transfer of other real estate owned			0	(4,554)
Net gains on sale of loans			(357)	(85)
Proceeds from sales of loans			6,345	2,850
Originations of loans held for sale			(5,988)	(2,764)
Amortization on alternative energy partnerships, venture capital and other investments			22,387	26,728
Net gain on sales and calls of securities			(853)	(1,153)
Amortization/accretion of security premiums/discounts, net			4,322	3,953
Loss on sales or disposal of fixed assets			55	45
Unrealized loss on equity securities	900	(5,800)	3,631	323
Stock-based compensation and stock issued to officers as compensation			3,302	3,344
Net change in accrued interest receivable and other assets			(4,966)	(10,592)
Net change in other liabilities			(14,433)	(1,330)
Net cash provided by operating activities			166,377	172,231
Cash Flows from Investing Activities
Purchase of investment securities available-for-sale			(244,567)	(216,745)
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			247,508	427,139
Purchase of Federal Home Loan Bank stock			0	(840)
Redemptions of Federal Home Loan Bank stock			0	1,680
Net increase in loans			(61,195)	(536,212)
Purchase of premises and equipment			(1,787)	(3,316)
Proceeds from sales of other real estate owned			0	2,246
Net increase in investment in affordable housing and alternative energy partnerships			(10,618)	(38,331)
Net cash used for investing activities			(49,557)	(253,728)
Cash Flows from Financing Activities
Net increase in deposits			428,291	1,589,416
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			(49,198)	(49,332)
Proceeds from other borrowings			0	91
Purchases of treasury stock			(63,529)	(12,880)
Repayment of short-term borrowings			0	(25,683)
Proceeds from shares issued under Dividend Reinvestment Plan			1,725	1,707
Taxes paid related to net share settlement of RSUs			(2,594)	(1,899)
Net cash provided by financing activities			184,695	1,061,420
Decrease in cash, cash equivalents, and restricted cash			301,515	979,923
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	$ 1,722,593	$ 1,573,701	1,722,593	1,573,701	$ 1,421,078
Supplemental disclosure of cash flow information
Interest			44,669	94,251
Income taxes paid			36,791	32,104
Non-cash investing and financing activities:
Net change in unrealized holding loss on securities available-for-sale, net of tax			(4,639)	10,564
Net change in unrealized holding loss on cash flow hedge derivatives			$ 1,702	$ (4,513)