Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets
Interest-earning deposits with banks	$ 34,332	$ 17,407
Debt securities available for sale	2,864,418	3,167,448
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	224,327	260,180
Interest-earning deposits with banks	34,332	17,407
Debt securities available for sale	2,864,418	3,167,448
FHLB stock	29,800	25,960
Loans held for sale	12,189	3,849
Loans	8,745,513	8,316,946
Interest rate contracts	17,857	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	15,691
Liabilities
Deposits	388,103	407,659
FHLB Advances	396,344	400,085
Repurchase agreements	50,226	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,397	34,897
Interest rate contracts	17,858	7,033
Reported Value Measurement [Member]
Assets
Cash and due from banks	224,327	260,180
Interest-earning deposits with banks	34,332	17,407
Debt securities available for sale	2,864,418	3,167,448
FHLB stock	29,800	25,960
Loans held for sale	12,189	3,849
Loans	8,566,473	8,308,142
Interest rate contracts	17,857	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	15,691
Liabilities
Deposits	391,496	414,443
FHLB Advances	495,496	399,523
Repurchase agreements	50,226	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,370	35,462
Interest rate contracts	17,858	7,033
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	224,327	260,180
Interest-earning deposits with banks	34,332	17,407
Debt securities available for sale	249	248
FHLB stock	0	0
Loans held for sale	0	0
Loans	0	0
Interest rate contracts	0	0
Interest Rate Cash Flow Hedge Asset at Fair Value	0
Liabilities
Deposits	0	0
FHLB Advances	0	0
Repurchase agreements	0	0
Subordinated Debt Obligations, Fair Value Disclosure	0	0
Interest rate contracts	0	0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Debt securities available for sale	2,864,169	3,167,200
FHLB stock	29,800	25,960
Loans held for sale	12,189	3,849
Loans	0	0
Interest rate contracts	17,857	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	15,691
Liabilities
Deposits	388,103	407,659
FHLB Advances	396,344	400,085
Repurchase agreements	50,226	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,397	34,897
Interest rate contracts	17,858	7,033
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Debt securities available for sale	0	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	8,745,513	8,316,946
Interest rate contracts	0	0
Interest Rate Cash Flow Hedge Asset at Fair Value	0
Liabilities
Deposits	0	0
FHLB Advances	0	0
Repurchase agreements	0	0
Subordinated Debt Obligations, Fair Value Disclosure	0	0
Interest rate contracts	$ 0	$ 0