Fair Value (Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities		$ 2,308,812	$ 2,093,404
Held to maturity securities		2,497,558	2,370,388
Derivative financial instruments	[1]	43,903	23,251
Derivative financial instruments	[1]	43,184	23,968
Total Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold		466,587	869,429
Available for sale securities		2,308,812	2,093,404
Held to maturity securities		2,569,084	2,375,851
Loans, net		16,174,870	15,427,803
Loans held for sale		42,297	20,434
Derivative financial instruments		43,903	23,251
Deposits		18,837,146	18,327,425
Federal funds purchased		10,575	10,100
Securities sold under agreements to repurchase		409,532	513,544
FHLB borrowings		675,000	900,000
Long-term debt		474,888	488,711
Derivative financial instruments		43,184	23,968
Total Fair Value [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold		466,587	869,429
Available for sale securities		1,212	2,757
Federal funds purchased		10,575	10,100
Securities sold under agreements to repurchase		409,532	513,544
FHLB borrowings		675,000	900,000
Total Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale securities		2,307,600	2,090,647
Held to maturity securities		2,569,084	2,375,851
Loans, net		116,516	93,602
Loans held for sale		42,297	20,434
Derivative financial instruments		43,903	23,251
Long-term debt		474,888	488,711
Derivative financial instruments		43,184	23,968
Total Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net		16,058,354	15,334,201
Deposits		18,837,146	18,327,425
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash, interest-bearing bank deposits, and federal funds sold		466,587	869,429
Available for sale securities		2,308,812	2,093,404
Held to maturity securities		2,497,558	2,370,388
Loans, net		15,809,710	15,522,135
Loans held for sale		42,297	20,434
Derivative financial instruments		43,903	23,251
Deposits		18,816,869	18,348,912
Federal funds purchased		10,575	10,100
Securities sold under agreements to repurchase		409,532	513,544
FHLB borrowings		675,000	900,000
Long-term debt		468,028	490,145
Derivative financial instruments		$ 43,184	$ 23,968

[1] For further disaggregation of derivative assets and liabilities, see Note 6 - Derivatives.