Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities
Net income	$ 63,816,000	$ 48,941,000
Adjustments to reconcile net income to net cash provided by operating activities:
Reversal for credit losses	(3,000,000)	(2,500,000)
Provision for losses on other real estate owned	33,000	272,000
Deferred tax liability	3,597,000	14,283,000
Depreciation and amortization	2,009,000	1,769,000
Net gains on sale and transfer of other real estate owned	(258,000)	(219,000)
Proceeds from sales of loans	8,000,000	7,500,000
Amortization on alternative energy partnerships, venture capital and other investments	(12,000)	187,000
Net loss/(gain) on sales and calls of securities		438,000
Amortization/accretion of security premiums/discounts, net	882,000	727,000
Unrealized loss on equity securities	3,847,000
Write-down on impaired securities		28,000
Stock based compensation and stock issued to officers as compensation	1,499,000	1,183,000
Net change in accrued interest receivable and other assets	7,870,000	(5,617,000)
Gain on acquisition	(340,000)
Net change in other liabilities	(2,995,000)	(12,926,000)
Net cash provided by operating activities	84,948,000	54,066,000
Cash Flows from Investing Activities
Purchase of investment securities available-for-sale	(125,714,000)	(99,965,000)
Proceeds from sale of investment securities available-for-sale		99,541,000
Proceeds from repayments, maturities and calls of investment securities available-for-sale	173,915,000	85,439,000
Redemptions of Federal Home Loan Bank stock	5,835,000
Net increase in loans	(141,205,000)	(170,843,000)
Purchase of premises and equipment	(638,000)	(1,016,000)
Proceeds from sales of other real estate owned	1,480,000	878,000
Net (increase)/decrease in investment in affordable housing and alternative energy partnerships	(10,673,000)	565,000
Net cash used for investing activities	(97,000,000)	(85,401,000)
Cash Flows from Financing Activities
Net increase/(decrease) in deposits	322,166,000	(87,333,000)
Net decrease in federal funds purchased and securities sold under agreements to repurchase		(200,000,000)
Advances from Federal Home Loan Bank	1,150,000,000	250,000,000
Repayment of Federal Home Loan Bank borrowings	(1,255,000,000)	(275,000,000)
Cash dividends paid	(19,469,000)	(16,756,000)
Proceeds from shares issued under Dividend Reinvestment Plan	664,000	617,000
Proceeds from exercise of stock options	838,000	422,000
Taxes paid related to net share settlement of RSUs	(3,223,000)	(5,118,000)
Net cash provided by (used in) financing activities	195,976,000	(333,169,000)
Increase/(decrease) in cash and cash equivalents	183,924,000	(364,504,000)
Cash and cash equivalents, beginning of the period	539,801,000	1,185,084,000
Cash and cash equivalents, end of the period	723,725,000	820,580,000
Supplemental disclosure of cash flow information
Interest	22,509,000	20,495,000
Income taxes paid	3,658,000	15,896,000
Non-cash investing and financing activities:
Net change in unrealized holding loss on securities available-for-sale, net of tax	(11,514,000)	(226,000)
Net change in unrealized holding loss on cash flow hedge derivatives	2,193,000	299,000
Transfers to other real estate owned from loans held for investment	715,000	726,000
Loans transferred from held for investment to held for sale, net		$ 5,835,000