Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Activities:
Net income	$ 255,439	$ 207,127	$ 204,729
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	40,900	56,350	49,300
Deferred tax (benefit) expense	(9,074)	17,700	(15,513)
Depreciation and amortization	37,172	36,449	34,678
Amortization of earning assets and funding premium/discount, net	45,444	57,331	54,555
Stock-based compensation	12,276	11,438	10,935
Gain on sale, net of write-down, on foreclosed and repossessed assets	(784)	(976)	(311)
(Gain on sale) write-down, net on premises and equipment	(15)	397	(244)
Impairment loss on securities recognized in earnings	126	149	110
Gain on the sale of investment securities, net	0	(414)	(609)
Increase in cash surrender value of life insurance policies	(14,627)	(14,759)	(13,020)
Mortgage banking activities	(9,937)	(14,635)	(7,795)
Proceeds from sale of loans held for sale	333,027	438,925	452,590
Originations of loans held for sale	(287,634)	(452,886)	(449,048)
Net decrease (increase) in derivative contract assets net of liabilities	32,763	27,929	(6,489)
Gain (Loss) on Disposition of Other Assets	0	7,331	0
Net (increase) decrease in accrued interest receivable and other assets	(19,790)	54,269	(44,554)
Net increase (decrease) in accrued expenses and other liabilities	29,680	(18,918)	33,478
Net cash provided by operating activities	444,966	398,145	302,792
Investing Activities:
Net decrease (increase) in interest-bearing deposits	3,833	126,446	(23,212)
Purchases of available-for-sale securities	(660,106)	(980,870)	(903,240)
Proceeds from maturities and principal payments of available-for-sale securities	984,732	672,965	558,301
Proceeds from sales of available-for-sale securities	0	259,283	123,270
Purchases of held-to-maturity securities	(1,043,278)	(1,066,156)	(761,033)
Proceeds from maturities and principal payments of held-to-maturity securities	687,439	795,953	681,124
Net proceeds (purchase) of Federal Home Loan Bank stock	43,080	(6,299)	4,943
Purchases of intercompany debt securities	873	(381)	458
Net increase in loans	(549,213)	(1,440,141)	(1,813,811)
Proceeds from loans not originated for sale	14,679	34,170	33,644
Purchase of life insurance policies	0	0	(50,000)
Proceeds from life insurance policies	746	0	3,912
Proceeds from the sale of foreclosed properties and repossessed assets	7,603	9,205	10,511
Proceeds from the sale of premises and equipment	3,357	1,550	650
Additions to premises and equipment	(28,546)	(40,731)	(36,115)
Proceeds from Sale of Other Assets	7,581	0	0
Acquisition of business, net cash acquired	0	0	1,396,414
Net cash provided by (used for) investing activities	(527,220)	(1,635,006)	(774,184)
Financing Activities:
Net increase in deposits	1,690,197	1,351,609	853,921
Proceeds from Other Debt	0	5,000	0
Proceeds from Federal Home Loan Bank advances	12,255,000	19,630,000	13,505,000
Repayments of Federal Home Loan Bank advances	(13,420,791)	(19,451,219)	(13,700,279)
Net decrease in securities sold under agreements to repurchase and other borrowings	(306,257)	(201,874)	(99,356)
Payments for Repurchase of Redeemable Preferred Stock	(122,710)	0	0
Proceeds from Issuance of Redeemable Preferred Stock	145,056	0	0
Dividends paid to common shareholders	(94,630)	(89,522)	(80,964)
Dividends paid to preferred shareholders	(8,096)	(8,096)	(8,711)
Exercise of stock options	8,259	11,762	3,060
Excess tax benefits from stock-based compensation	0	3,204	2,338
Common stock repurchased	(11,585)	(11,206)	(12,564)
Shares acquired related to employee share-based compensation plans	(11,694)	(11,664)	(5,251)
Common stock warrants repurchased	0	(163)	(23)
Net cash (used for) provided by financing activities	122,749	1,227,831	457,171
Net decrease in cash and due from banks	40,495	(9,030)	(14,221)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Beginning Balance	190,663	199,693	213,914
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Ending Balance	231,158	190,663	199,693
Supplemental disclosure of cash flow information:
Interest paid	114,046	102,438	95,428
Income taxes paid	109,059	80,143	106,991
Noncash investing and financing activities:
Transfer of loans and leases to foreclosed properties and repossessed assets	8,972	6,769	8,714
Transfer of loans from portfolio to loans held for sale	7,234	39,383	585
Deposits assumed in business acquisition	0	0	1,446,899
Preferred stock conversion	$ 0	$ 0	$ 28,939