Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash Flows from Operating Activities
Net income	$ 138,923	$ 137,480
Adjustments to reconcile net income to net cash provided by operating activities:
Reversal for credit losses	0	(3,000)
Provision for losses on other real estate owned	494	0
Deferred tax liability	8,592	2,432
Depreciation and amortization	3,308	3,868
Amortization of right-of-use asset	4,146	0
Change in operating lease liabilities	(3,477)	0
Net gains on sale and transfer of other real estate owned	(193)	(459)
Proceeds from sales of loans	0	8,000
Amortization on alternative energy partnerships, venture capital and other investments	19,929	(405)
Net gain on sales and calls of securities	(13)	0
Amortization/accretion of security premiums/discounts, net	1,165	1,719
Unrealized (gain)/loss on equity securities	(7,400)	4,971
Stock based compensation and stock issued to officers as compensation	3,808	4,054
Net change in accrued interest receivable and other assets	(46,292)	(8,043)
Gain on acquisition	0	(340)
Net change in other liabilities	50,533	(129)
Net cash provided by operating activities	173,523	150,148
Cash Flows from Investing Activities
Decrease in interest-bearing deposits	0	5,000
Purchase of investment securities available-for-sale	(425,661)	(448,805)
Proceeds from sale of investment securities available-for-sale	50,225	0
Proceeds from repayments, maturities and calls of investment securities available-for-sale	183,563	257,339
Purchase of Federal Home Loan Bank stock	(975)	(5,430)
Redemptions of Federal Home Loan Bank stock	975	11,265
Net increase in loans	(597,827)	(474,900)
Purchase of premises and equipment	(2,695)	(2,706)
Proceeds from sales of other real estate owned	1,905	2,785
Net increase in investment in affordable housing and alternative energy partnerships	(23,540)	(19,201)
Net cash used for investing activities	(814,030)	(674,653)
Cash Flows from Financing Activities
Net increase in deposits	660,368	414,198
Net decrease in federal funds purchased and securities sold under agreements to repurchase	0	(50,000)
Repayment of Federal Home Loan Bank borrowings	(3,180,000)	(2,400,000)
Cash dividends paid	(49,721)	(38,966)
Repayment of other borrowings	(19,687)	0
Proceeds from other borrowings	19,211	20,000
Purchases of treasury stock	(31,609)	0
Proceeds from shares issued under Dividend Reinvestment Plan	1,681	1,325
Proceeds from exercise of stock options	0	838
Taxes paid related to net share settlement of RSUs	(2,300)	(3,550)
Net cash provided by financing activities	597,943	393,845
Decrease in cash, cash equivalents, and restricted cash	(42,564)	(130,660)
Cash, cash equivalents, and restricted cash, beginning of the period	600,290	534,801
Cash, cash equivalents, and restricted cash, end of the period	557,726	404,141
Supplemental disclosure of cash flow information
Interest	87,636	49,606
Income taxes paid	33,807	31,589
Non-cash investing and financing activities:
Net change in unrealized holding loss on securities available-for-sale, net of tax	19,974	(14,265)
Net change in unrealized holding loss on cash flow hedge derivatives	(3,326)	2,929
Transfers to other real estate owned from loans held for investment	860	715
Business Acquired During the Period [Member]
Cash Flows from Financing Activities
Advances from Federal Home Loan Bank	$ 3,200,000	$ 2,450,000