Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash Flows from Operating Activities
Net income	$ 54,321		$ 72,244	$ 101,173	$ 138,923
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	25,000	$ 25,000	0	50,000	0
Provision for losses on other real estate owned				717	494
Deferred tax provision				(4,896)	8,592
Depreciation and amortization				3,688	3,308
Amortization of right-of-use asset				4,249	4,146
Change in operating lease liabilities				535	(3,477)
Net gains on sale and transfer of other real estate owned				(4,554)	(193)
Net gains on sale of loans				(85)	0
Proceeds from sales of loans				2,850	0
Originations of loans held for sale				(2,764)	0
Amortization on alternative energy partnerships, venture capital and other investments				26,728	19,929
Net gain on sales and calls of securities				(1,153)	(13)
Amortization/accretion of security premiums/discounts, net				3,953	1,165
Loss on sales or disposal of fixed assets				45	0
Unrealized loss/(gain) on equity securities	(5,800)		(3,200)	323	(7,400)
Stock based compensation and stock issued to officers as compensation				3,344	3,808
Net change in accrued interest receivable and other assets				(10,592)	(46,292)
Net change in other liabilities				(1,330)	50,533
Net cash provided by operating activities				172,231	173,523
Cash Flows from Investing Activities
Purchase of investment securities available-for-sale				(216,745)	(425,661)
Proceeds from sale of investment securities available-for-sale				107,539	50,225
Proceeds from sale of equity securities				3,112	0
Proceeds from repayments, maturities and calls of investment securities available-for-sale				427,139	183,563
Purchase of Federal Home Loan Bank stock				(840)	(975)
Redemptions of Federal Home Loan Bank stock				1,680	975
Net increase in loans				(536,212)	(597,827)
Purchase of premises and equipment				(3,316)	(2,695)
Proceeds from sales of other real estate owned				2,246	1,905
Net increase in investment in affordable housing and alternative energy partnerships				(38,331)	(23,540)
Net cash used for investing activities				(253,728)	(814,030)
Cash Flows from Financing Activities
Net increase in deposits				1,589,416	660,368
Advances from Federal Home Loan Bank				1,450,000	3,200,000
Repayment of Federal Home Loan Bank borrowings				(1,890,000)	(3,180,000)
Cash dividends paid				(49,332)	(49,721)
Repayment of other borrowings				0	(19,687)
Proceeds from other borrowings				91	19,211
Purchases of treasury stock				(12,880)	(31,609)
Repayment of short-term borrowings				(25,683)	0
Proceeds from shares issued under Dividend Reinvestment Plan				1,707	1,681
Taxes paid related to net share settlement of RSUs				(1,899)	(2,300)
Net cash provided by financing activities				1,061,420	597,943
Increase/(Decrease) in cash, cash equivalents, and restricted cash				979,923	(42,564)
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	$ 1,573,701		$ 557,726	1,573,701	557,726	$ 593,778
Supplemental disclosure of cash flow information
Interest				94,251	87,636
Income taxes paid				32,104	33,807
Non-cash investing and financing activities:
Net change in unrealized holding loss on securities available-for-sale, net of tax				10,564	19,974
Net change in unrealized holding loss on cash flow hedge derivatives				(4,513)	(3,326)
Transfers to other real estate owned from loans held for investment				$ 0	$ 860