Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets
Interest-earning deposits with banks	$ 33,482	$ 17,407
Debt securities available for sale	3,027,270	3,167,448
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	178,591	260,180
Interest-earning deposits with banks	33,482	17,407
Debt securities available for sale	3,027,270	3,167,448
FHLB stock	25,960	25,960
Loans held for sale	4,017	3,849
Loans	8,541,649	8,316,946
Interest rate contracts	8,815	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	6,268
Liabilities
Deposits	406,652	407,659
FHLB Advances	390,988	400,085
Repurchase agreements	23,018	61,094
Subordinated Debt Obligations, Fair Value Disclosure	36,053	34,897
Interest rate contracts	8,815	7,033
Reported Value Measurement [Member]
Assets
Cash and due from banks	178,591	260,180
Interest-earning deposits with banks	33,482	17,407
Debt securities available for sale	3,027,270	3,167,448
FHLB stock	25,600	25,960
Loans held for sale	4,017	3,849
Loans	8,437,524	8,308,142
Interest rate contracts	8,815	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	6,268
Liabilities
Deposits	411,945	414,443
FHLB Advances	390,510	399,523
Repurchase agreements	23,018	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,416	35,462
Interest rate contracts	8,815	7,033
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	178,591	260,180
Interest-earning deposits with banks	33,482	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	3,027,021	3,167,200
FHLB stock	25,960	25,960
Loans held for sale	4,017	3,849
Loans	0	0
Interest rate contracts	8,815	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	6,268
Liabilities
Deposits	406,652	407,659
FHLB Advances	390,988	400,085
Repurchase agreements	23,018	61,094
Subordinated Debt Obligations, Fair Value Disclosure	36,053	34,897
Interest rate contracts	8,815	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	8,541,649	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