Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Interest-earning deposits with banks	$ 21,456	$ 97,918
Debt Securities, Available-for-sale	2,921,114	2,737,751
Equity Securities, FV-NI	4,901	5,080
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	220,706	244,615
Interest-earning deposits with banks	21,456	97,918
Debt Securities, Available-for-sale	2,921,114	2,737,751
Equity Securities, FV-NI	4,901	5,080
FHLB stock	16,640	10,440
Loans held for sale	5,275	5,766
Loans	8,425,433	8,055,817
Interest rate contracts	10,479	6,707
Liabilities
Deposits	423,165	483,095
FHLB Advances	166,999	12,281
Repurchase agreements	62,197	79,070
Interest rate contracts	10,478	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,001	35,895
Junior subordinated debentures, fair value disclosure		8,248
Reported Value Measurement [Member]
Assets
Cash and due from banks	220,706	244,615
Interest-earning deposits with banks	21,456	97,918
Debt Securities, Available-for-sale	2,921,114	2,737,751
Equity Securities, FV-NI	4,901	5,080
FHLB stock	16,640	10,440
Loans held for sale	5,275	5,766
Loans	8,430,530	8,283,011
Interest rate contracts	10,479	6,707
Liabilities
Deposits	431,496	491,045
FHLB Advances	166,536	11,579
Repurchase agreements	62,197	79,059
Interest rate contracts	10,478	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,508	35,647
Junior subordinated debentures, fair value disclosure		8,248
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	220,706	244,615
Interest-earning deposits with banks	21,456	97,918
Debt Securities, Available-for-sale	247	248
Equity Securities, FV-NI	4,901	5,080
FHLB stock	0	0
Loans held for sale	0	0
Loans	0	0
Interest rate contracts	0	0
Liabilities
Deposits	0	0
FHLB Advances	0	0
Repurchase agreements	0	0
Interest rate contracts	0	0
Subordinated Debt Obligations, Fair Value Disclosure	0	0
Junior subordinated debentures, fair value disclosure		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	2,920,867	2,737,503
Equity Securities, FV-NI	0	0
FHLB stock	16,640	10,440
Loans held for sale	5,275	5,766
Loans	0	0
Interest rate contracts	10,479	6,707
Liabilities
Deposits	423,165	483,095
FHLB Advances	166,999	12,281
Repurchase agreements	62,197	79,070
Interest rate contracts	10,478	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,001	35,895
Junior subordinated debentures, fair value disclosure		8,248
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
Equity Securities, FV-NI	0	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	8,425,433	8,055,817
Interest rate contracts	0	0
Liabilities
Deposits	0	0
FHLB Advances	0	0
Repurchase agreements	0	0
Interest rate contracts	0	0
Subordinated Debt Obligations, Fair Value Disclosure	$ 0	0
Junior subordinated debentures, fair value disclosure		$ 0