Fair Value Measurements Details of Book Value and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Available for sale investment securities	$ 2,561,516	$ 2,559,227
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	99,803	118,763
Interest-bearing deposits with other banks	582,845	233,763
Federal Reserve Bank and Federal Home Loan Bank stock	62,951	57,489
Loans held for sale	23,049	28,697
Available for sale investment securities	2,561,516	2,559,227
Net Loans	15,314,654	14,530,593
Accrued interest receivable	50,082	46,294
Other financial assets	219,434	206,132
Demand and savings deposits	13,274,319	12,259,622
Brokered Deposits	109,936	0
Time deposits	2,757,525	2,753,242
Short-term borrowings	298,751	541,317
Accrued interest payable	10,568	9,632
Other financial liabilities	234,160	216,080
Federal Home Loan Bank advances and other long-term debt	1,038,159	929,403
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, FinancialStatement Captions[Line Items]
Cash and due from banks	99,803	118,763
Interest-bearing deposits with other banks	582,845	233,763
Federal Reserve Bank and Federal Home Loan Bank stock	62,951	57,489
Loans held for sale	23,049	28,697
Available for sale investment securities	2,561,516	2,559,227
Net Loans	15,086,654	14,387,454
Accrued interest receivable	50,082	46,294
Other financial assets	219,434	206,132
Demand and savings deposits	13,274,319	12,259,622
Brokered Deposits	109,936	0
Time deposits	2,759,913	2,769,757
Short-term borrowings	298,751	541,317
Accrued interest payable	10,568	9,632
Other financial liabilities	234,160	216,080
Federal Home Loan Bank advances and other long-term debt	$ 1,035,053	$ 928,167