Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets
Interest-earning deposits with banks	$ 39,169	$ 97,918
Debt Securities, Available-for-sale	2,646,208	2,737,751
Equity Securities, FV-NI	4,963	5,080
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	224,370	244,615
Interest-earning deposits with banks	39,169	97,918
Debt Securities, Available-for-sale	2,646,208	2,737,751
Equity Securities, FV-NI	4,963	5,080
FHLB stock	13,960	10,440
Loans held for sale	6,773	5,766
Loans	8,381,155	8,055,817
Interest rate contracts	8,624	6,707
Liabilities
Deposits	442,561	10,524,135
FHLB Advances	100,102	12,281
Repurchase agreements	46,229	79,070
Interest rate contracts	8,624	6,714
Subordinated Debt Obligations, Fair Value Disclosure	34,986	35,895
Junior subordinated debentures, fair value disclosure		8,248
Reported Value Measurement [Member]
Assets
Cash and due from banks	224,370	244,615
Interest-earning deposits with banks	39,169	97,918
Debt Securities, Available-for-sale	2,646,208	2,737,751
Equity Securities, FV-NI	4,963	5,080
FHLB stock	13,960	10,440
Loans held for sale	6,773	5,766
Loans	8,373,957	8,283,011
Interest rate contracts	8,624	6,707
Liabilities
Deposits	450,602	10,532,085
FHLB Advances	99,549	11,579
Repurchase agreements	46,229	79,059
Interest rate contracts	8,624	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,555	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	224,370	244,615
Interest-earning deposits with banks	39,169	97,918
Debt Securities, Available-for-sale	247	248
Equity Securities, FV-NI	4,963	5,080
FHLB stock	0	0
Loans held for sale	0	0
Loans	0	0
Interest rate contracts	0	0
Liabilities
Deposits	0	10,041,040
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	2,645,961	2,737,503
Equity Securities, FV-NI	0	0
FHLB stock	13,960	10,440
Loans held for sale	6,773	5,766
Loans	0	0
Interest rate contracts	8,624	6,707
Liabilities
Deposits	442,561	483,095
FHLB Advances	100,102	12,281
Repurchase agreements	46,229	79,070
Interest rate contracts	8,624	6,714
Subordinated Debt Obligations, Fair Value Disclosure	34,986	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	8,381,155	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