Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Interest-earning deposits with banks	$ 87,124	$ 97,918
Available-for-sale Securities, Debt Securities	2,624,045	2,737,751
Marketable Securities, Equity Securities	5,000	5,080
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	206,532	244,615
Interest-earning deposits with banks	87,124	97,918
Available-for-sale Securities, Debt Securities	2,624,045	2,737,751
Marketable Securities, Equity Securities	5,000	5,080
FHLB stock	11,640	10,440
Loans held for sale	4,312	5,766
Loans	8,281,010	8,055,817
Interest rate contracts	7,406	6,707
Liabilities
Deposits	465,896	10,524,135
FHLB Advances	42,090	12,281
Repurchase agreements	24,247	79,070
Interest rate contracts	7,409	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,486	35,895
Junior subordinated debentures, fair value disclosure		8,248
Reported Value Measurement [Member]
Assets
Cash and due from banks	206,532	244,615
Interest-earning deposits with banks	87,124	97,918
Available-for-sale Securities, Debt Securities	2,624,045	2,737,751
Marketable Securities, Equity Securities	5,000	5,080
FHLB stock	11,640	10,440
Loans held for sale	4,312	5,766
Loans	8,259,804	8,283,011
Interest rate contracts	7,406	6,707
Liabilities
Deposits	474,000	10,532,085
FHLB Advances	41,564	11,579
Repurchase agreements	24,247	79,059
Interest rate contracts	7,409	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,601	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	206,532	244,615
Interest-earning deposits with banks	87,124	97,918
Available-for-sale Securities, Debt Securities	247	248
Marketable Securities, Equity Securities	5,000	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
Available-for-sale Securities, Debt Securities	2,623,798	2,737,503
Marketable Securities, Equity Securities	0	0
FHLB stock	11,640	10,440
Loans held for sale	4,312	5,766
Loans	0	0
Interest rate contracts	7,406	6,707
Liabilities
Deposits	465,896	483,095
FHLB Advances	42,090	12,281
Repurchase agreements	24,247	79,070
Interest rate contracts	7,409	6,714
Subordinated Debt Obligations, Fair Value Disclosure	35,486	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
Available-for-sale Securities, Debt Securities	0	0
Marketable Securities, Equity Securities	0	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	8,281,010	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