Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Cash Flows from Operating Activities
Net income	$ 279,135	$ 271,885	$ 176,042
Reversal for credit losses	(7,000)	(4,500)	(2,500)
Provision for losses on other real estate owned	681	0	691
Deferred tax provision	9,825	2,343	34,554
Depreciation and amortization	6,756	7,314	7,265
Amortization of right-of-use asset	8,366	0	0
Change in operating lease liabilities	(7,157)	0	0
Net gains on sale and transfers of other real estate owned	(212)	(1,187)	(2,661)
Net gains on sale of loans	(804)	0	0
Proceeds from sale of loans	75,257	8,000	7,500
Originations of loans held for sale	(2,241)	0	0
Loss on sales or disposal of fixed assets	14	107	0
Amortization of alternative energy partnerships, venture capital and other investments	39,898	40,871	4,572
Gain on sales and calls of securities	(211)	(22)	(1,006)
Other non-cash interest income	0	(1,576)	(1,740)
Amortization of security premiums, net	3,834	3,018	2,945
(Gain)/loss on equity securities	(5,736)	2,787	0
Stock based and stock issued to officers and directors compensation expense	7,350	7,974	5,734
Net change in accrued interest receivable and other assets	6,163	(13,984)	25,747
Gain from acquisition	0	(340)	(5,628)
Net change in other liabilities	21,061	13,848	(2,641)
Net cash provided by operating activities	434,979	336,538	248,874
Cash Flows from Investing Activities
Decrease in interest bearing deposits	0	5,000	0
Purchase of investment securities available-for-sale	(770,206)	(497,787)	(607,574)
Proceeds from repayment, maturity and call of investment securities available-for-sale	296,721	447,773	562,595
Proceeds from sale of investment securities available-for-sale	293,849	99,899	111,704
Proceeds from sale of equity securities	2,829	0	0
Purchase of Federal Home Loan Bank stock	(1,815)	(5,430)	(8,160)
Redemption of Federal Home Loan Bank stock	975	11,265	13,482
Redemption of Federal Reserve Bank stock	0	0	8,733
Net increase in loans	(1,147,019)	(1,125,623)	(963,858)
Purchase of premises and equipment	(7,133)	(6,670)	(3,188)
Proceeds from sales of premises and equipment	0	0	5,598
Proceeds from sales of other real estate owned	2,822	3,820	18,357
Increase in investment in affordable housing and alternative energy partnerships	(52,697)	(66,574)	(40,284)
Acquisitions, net of cash acquired	0	0	(1,392)
Net cash used in investing activities	(1,381,674)	(1,134,327)	(903,987)
Cash Flows from Financing Activities
Net increase in deposits	989,942	1,012,284	201,224
Net decrease in federal funds purchased and securities sold under agreements to repurchase	0	(100,000)	(250,000)
Advances from Federal Home Loan Bank	4,355,000	5,130,000	4,823,000
Repayment of Federal Home Loan Bank borrowings	(4,215,000)	(5,030,000)	(4,773,000)
Cash dividends	(99,131)	(83,428)	(69,888)
Purchase of treasury stock	(36,301)	(42,648)	0
Proceeds from issuance of short-term borrowings	25,683	0	0
Proceeds from issuance of long-term debt and other borrowings	0	0	75,000
Repayment of long-term debt and other borrowings	(81,065)	(23,040)	0
Proceeds from shares issued to Dividend Reinvestment Plan	3,366	2,822	2,528
Proceeds from exercise of stock options	0	838	1,094
Taxes paid related to net share settlement of RSUs	(2,311)	(3,550)	(5,128)
Net cash provided by financing activities	940,183	863,278	4,830
Increase/(Decrease) in cash, cash equivalents and restricted cash	(6,512)	65,489	(650,283)
Cash, cash equivalents and restricted cash, beginning of the year	600,290	534,801	1,185,084
Cash, cash equivalents and restricted cash, end of the year	593,778	600,290	534,801
Supplemental disclosure of cash flow information
Interest	182,527	116,524	81,069
Income taxes	61,548	65,866	76,709
Non-cash investing and financing activities:
Net change in unrealized holding (loss)/gain on securities available-for-sale, net of tax	23,479	(7,949)	485
Net change in unrealized gain on interest rate swaps designated as cash flow hedges	(3,171)	1,525	719
Transfers to other real estate owned from loans held for investment	860	5,476	1,243
Loans transferred to loans held for sale	75,285	0	8,000
Loans to facilitate the sale of other real estate owned	0	0	10,500
Issuance of stock related to acquisition	0	0	34,862
Business Acquired During the Period [Member]
Supplemental disclosure for acquisitions
Cash and cash equivalents	0	0	283,932
Short-term investments	0	0	5,000
Securities available-for-sale	0	0	88,044
FHLB and FRB stock	0	0	19,890
Loans	0	0	705,792
Premises and equipment	0	0	6,239
Cash surrender value of life insurance	0	0	46,083
Deferred tax assets, net	0	0	40,690
Core deposit intangible	0	0	6,122
Accrued interest receivable and other assets	0	0	10,689
Total assets acquired	0	0	1,212,481
Deposits	0	0	813,888
Advances from Federal Home Loan Bank	0	0	30,000
Accrued interest payable and other liabilities	0	0	8,512
Total liabilities assumed	0	0	852,400
Net assets acquired	0	0	360,081
Cash paid	0	0	285,324
Fair value of common stock issued	0	0	34,862
Total consideration paid	$ 0	$ 0	$ 320,186