Loans and Allowance for Loan Losses (Schedule Of Allowances For Loan Losses And Recorded Investment In Loans) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Allowance for loan losses:
Beginning balance, allowance	$ 249,268,000	$ 251,758,000	$ 251,758,000
Charge-offs	(14,381,000)	(12,735,000)
Recoveries	10,101,000	5,817,000
Provision for loan losses	12,776,000	8,674,000
Ending balance, allowance	257,764,000	253,514,000	249,268,000
Ending balance: individually evaluated for impairment, allowance	18,942,000	19,707,000
Ending balance: collectively evaluated for impairment, allowance	238,822,000	233,807,000
Total loans	24,906,998,000	24,284,188,000	24,812,795,000
Ending balance: individually evaluated for impairment, loans	191,652,000	234,756,000
Ending balance: collectively evaluated for impairment, loans	24,715,346,000	24,049,432,000
Purchased credit-impaired loans	0	0
Allowance for purchased credit-impaired loans	0	0
Deferred fees and costs, net	24,000,000	25,700,000	25,300,000
Commercial Real Estate
Allowance for loan losses:
Beginning balance, allowance	74,998,000	81,816,000	81,816,000
Charge-offs	(1,911,000)	(1,908,000)
Recoveries	5,723,000	2,889,000
Provision for loan losses	(4,819,000)	(4,483,000)
Ending balance, allowance	73,991,000	78,314,000	74,998,000
Ending balance: individually evaluated for impairment, allowance	3,740,000	6,917,000
Ending balance: collectively evaluated for impairment, allowance	70,251,000	71,397,000
Total loans	6,835,727,000	7,467,288,000
Ending balance: individually evaluated for impairment, loans	49,221,000	79,203,000
Ending balance: collectively evaluated for impairment, loans	6,786,506,000	7,388,085,000
Commercial & Industrial
Allowance for loan losses:
Beginning balance, allowance	126,803,000	125,778,000	125,778,000
Charge-offs	(8,015,000)	(6,893,000)
Recoveries	3,112,000	1,824,000
Provision for loan losses	12,845,000	6,387,000
Ending balance, allowance	134,745,000	127,096,000	126,803,000
Ending balance: individually evaluated for impairment, allowance	14,405,000	11,085,000
Ending balance: collectively evaluated for impairment, allowance	120,340,000	116,011,000
Total loans	12,101,917,000	11,732,701,000
Ending balance: individually evaluated for impairment, loans	112,823,000	120,470,000
Ending balance: collectively evaluated for impairment, loans	11,989,094,000	11,612,231,000
Retail
Allowance for loan losses:
Beginning balance, allowance	47,467,000	44,164,000	44,164,000
Charge-offs	(4,455,000)	(3,934,000)
Recoveries	1,266,000	1,104,000
Provision for loan losses	4,750,000	6,770,000
Ending balance, allowance	49,028,000	48,104,000	$ 47,467,000
Ending balance: individually evaluated for impairment, allowance	797,000	1,705,000
Ending balance: collectively evaluated for impairment, allowance	48,231,000	46,399,000
Total loans	5,969,354,000	5,084,199,000
Ending balance: individually evaluated for impairment, loans	29,608,000	35,083,000
Ending balance: collectively evaluated for impairment, loans	$ 5,939,746,000	$ 5,049,116,000