Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets
Interest-earning deposits with banks	$ 20,144	$ 17,407
Debt securities available for sale	3,367,572	3,167,448
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	278,461	260,180
Interest-earning deposits with banks	20,144	17,407
Debt securities available for sale	3,367,572	3,167,448
FHLB stock	29,680	25,960
Loans held for sale	15,036	3,849
Loans	8,895,564	8,316,946
Interest rate contracts	24,045	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	19,703
Liabilities
Deposits	361,195	407,659
FHLB Advances	493,736	400,085
Repurchase agreements	24,489	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,255	34,897
Interest rate contracts	25,046	7,033
Reported Value Measurement [Member]
Assets
Cash and due from banks	278,461	260,180
Interest-earning deposits with banks	20,144	17,407
Debt securities available for sale	3,367,572	3,167,448
FHLB stock	29,680	25,960
Loans held for sale	15,036	3,849
Loans	8,673,695	8,308,142
Interest rate contracts	25,045	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	19,703
Liabilities
Deposits	366,773	414,443
FHLB Advances	492,482	399,523
Repurchase agreements	24,489	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,323	35,462
Interest rate contracts	25,046	7,033
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	278,461	260,180
Interest-earning deposits with banks	20,144	17,407
Debt securities available for sale	250	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	3,367,322	3,167,200
FHLB stock	29,680	25,960
Loans held for sale	15,036	3,849
Loans	0	0
Interest rate contracts	24,045	7,033
Interest Rate Cash Flow Hedge Asset at Fair Value	19,703
Liabilities
Deposits	361,195	407,659
FHLB Advances	493,736	400,085
Repurchase agreements	24,489	61,094
Subordinated Debt Obligations, Fair Value Disclosure	35,255	34,897
Interest rate contracts	25,046	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	8,895,564	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