Consolidated Statements of Cash Flows	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Cash Flows from Operating Activities
Net income	$ 175,099,000	$ 161,109,000	$ 137,830,000
Adjustments to reconcile net income to net cash provided by operating activities:
Credit for loan losses	(15,650,000)	(11,400,000)	(10,800,000)
Provision for losses on other real estate owned	176,000	547,000	1,619,000
Deferred tax liability	15,949,000	2,004,000	31,304,000
Depreciation and amortization	7,490,000	7,574,000	7,868,000
Net gains on sale and transfers of other real estate owned	(546,000)	(2,012,000)	(4,065,000)
Net gains on sale of loans	(285,000)	(786,000)	(395,000)
Proceeds from sale of loans	20,079,000	32,530,000	19,287,000
Originations of loans held for sale	(12,665,000)	(37,447,000)	(19,865,000)
Income associated with debt redemption			(555,000)
Amortization on alternative energy partnerships, venture capital and other investments	28,897,000	25,058,000	436,000
Write-down on impaired securities	206,000	3,875,000	820,000
Gain on sales and calls of securities	(5,104,000)	(526,000)	(7,568,000)
Other non-cash interest income	(1,272,000)	(332,000)	(137,000)
Amortization of security premiums, net	6,371,000	5,140,000	2,849,000
Excess tax short-fall from stock options		5,348,000	1,285,000
Stock based and stock issued to officers and directors compensation expense	4,963,000	4,950,000	4,190,000
Net change in accrued interest receivable and other assets	13,478,000	(3,429,000)	(2,776,000)
Net change in other liabilities	(2,784,000)	(15,506,000)	(11,256,000)
Net cash provided by operating activities	234,402,000	176,697,000	150,071,000
Cash Flows from Investing Activities
(Increase)/decrease in short-term investments	(430,187,000)	(47,266,000)	32,260,000
Purchase of investment securities available-for-sale	(941,327,000)	(295,497,000)	(885,782,000)
Proceeds from maturity and call of investment securities available-for-sale	460,000,000	165,000,000	585,776,000
Proceeds from sale of investment securities available-for-sale	294,000	385,234,000	160,451,000
Purchase of mortgage-backed securities available-for-sale		(1,280,870,000)	(307,617,000)
Proceeds from repayment and sale of mortgage-backed securities available-for-sale	758,271,000	749,219,000	768,236,000
Purchase of Federal Home Loan Bank stock	(1,650,000)		(18,164,000)
Redemption of Federal Home Loan Bank stock	1,650,000	13,535,000	12,379,000
Net increase in loans	(1,051,952,000)	(829,501,000)	(824,558,000)
Purchase of premises and equipment	(3,523,000)	(3,518,000)	(4,777,000)
Proceeds from sales of premises and equipment	12,000	602,000
Proceeds from sales of other real estate owned	7,699,000	12,154,000	29,880,000
Increase in investment in affordable housing and alternative energy partnerships	(82,966,000)	(53,235,000)	(7,445,000)
Acquisition, net of cash acquired		6,572,000
Net cash used in investing activities	(1,283,679,000)	(1,177,571,000)	(459,361,000)
Cash Flows from Financing Activities
Net increase in deposits	1,166,044,000	1,305,255,000	802,281,000
Net decrease in federal funds purchased and securities sold under agreements to repurchase	(50,000,000)	(50,000,000)	(350,000,000)
Advances from Federal Home Loan Bank	3,555,000,000	5,092,000,000	9,822,400,000
Repayment of Federal Home Loan Bank borrowings	(3,480,000,000)	(5,242,000,000)	(9,918,600,000)
Cash dividends	(59,274,000)	(45,283,000)	(23,104,000)
Purchase of treasury stock	(54,441,000)	(59,412,000)
Repayment of long-term debt and other borrowings			(1,445,000)
Proceeds from shares issued to Dividend Reinvestment Plan	2,277,000	4,175,000	2,848,000
Proceeds from exercise of stock options	7,661,000	5,014,000	128,000
Taxes paid related to net share settlement of RSUs	(103,000)	(227,000)	(850,000)
Excess tax short-fall from share-based payment arrangements		(5,348,000)	(1,285,000)
Net cash provided by financing activities	1,087,164,000	1,004,174,000	332,373,000
Increase in cash and cash equivalents	37,887,000	3,300,000	23,083,000
Cash and cash equivalents, beginning of the year	180,130,000	176,830,000	153,747,000
Cash and cash equivalents, end of the year	218,017,000	180,130,000	176,830,000
Supplemental disclosure of cash flow information
Interest	81,793,000	72,870,000	78,366,000
Income taxes	38,671,000	69,074,000	60,225,000
Non-cash investing and financing activities:
Net change in unrealized holding gain/(loss) on securities available-for-sale, net of tax	3,886,000	(2,259,000)	26,557,000
Net change in unrealized gain/(loss) on interest rate swaps designated as cash flow hedges	825,000	(598,000)	(2,397,000)
Transfers to short-term investments from trading securities			4,936,000
Transfers to other real estate owned from loans held for investment	2,698,000	866,000	4,970,000
Loans transferred to loans held for sale	7,953,000	6,684,000	973,000
Loans to facilitate the sale of other real estate owned	2,616,000		413,000
Issuance of stock related to acquisition		82,857,000
Supplemental disclosure for acquisitions
Goodwill	$ 372,189,000	372,189,000
Asia Bancshares [Member]
Supplemental disclosure for acquisitions
Cash and cash equivalents		63,579,000
Securities available-for-sale		2,370,000
Loans		419,219,000
Premises and equipment		13,291,000
Other real estate owned		3,048,000
Goodwill		55,849,000
Core deposit intangible		1,302,000
Accrued interest receivable and other assets		2,884,000
Total assets acquired		561,542,000
Deposits		420,623,000
Accrued interest payable and other liabilities		1,056,000
Total liabilities assumed		421,679,000
Net assets acquired		139,863,000
Cash paid		57,006,000
Fair value of common stock issued		82,857,000
Total consideration paid		$ 139,863,000