Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Assets
Interest-earning deposits with banks	$ 22,578	$ 16,949
Securities available for sale	2,027,424	2,098,257
Liabilities
Other borrowings	0	8,248
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Assets
Cash and due from banks	149,610	171,221
Interest-earning deposits with banks	22,578	16,949
Securities available for sale	2,027,424	2,098,257
FHLB stock	10,242	33,365
Loans held for sale	6,637	1,116
Loans	5,677,462	5,375,809
FDIC loss-sharing asset	8,146	15,174
Interest rate contracts	14,548	11,800
Liabilities
Deposits	7,314,805	6,924,722
FHLB Advances	6,540	216,568
Repurchase agreements	73,182	105,080
Interest rate contracts	14,602	11,851
Other borrowings		8,248
Estimate of Fair Value, Fair Value Disclosure [Member]
Assets
Cash and due from banks	149,610	171,221
Interest-earning deposits with banks	22,578	16,949
Securities available for sale	2,027,424	2,098,257
FHLB stock	10,242	33,365
Loans held for sale	6,637	1,116
Loans	5,783,474	5,516,286
FDIC loss-sharing asset	2,140	4,054
Interest rate contracts	14,548	11,800
Liabilities
Deposits	7,312,329	6,921,804
FHLB Advances	7,198	217,296
Repurchase agreements	74,046	106,171
Interest rate contracts	14,602	11,851
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Assets
Cash and due from banks	149,610	171,221
Interest-earning deposits with banks	22,578	16,949
Securities available for sale	20,400	20,499
FHLB stock	0	0
Loans held for sale	0	0
Loans	0	0
FDIC loss-sharing asset	0	0
Interest rate contracts	0	0
Liabilities
Deposits	6,844,014	6,416,017
FHLB Advances	0	0
Repurchase agreements	0	0
Interest rate contracts	0	0
Other Liabilities, Fair Value Disclosure		0
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Securities available for sale	2,007,024	2,077,758
FHLB stock	10,242	33,365
Loans held for sale	6,637	1,116
Loans	0	0
FDIC loss-sharing asset	0	0
Interest rate contracts	14,548	11,800
Liabilities
Deposits	468,315	505,787
FHLB Advances	7,198	217,296
Repurchase agreements	74,046	106,171
Interest rate contracts	14,602	11,851
Other Liabilities, Fair Value Disclosure		8,248
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Securities available for sale	0	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	5,783,474	5,516,286
FDIC loss-sharing asset	2,140	4,054
Interest rate contracts	0	0
Liabilities
Deposits	0	0
FHLB Advances	0	0
Repurchase agreements	0	0
Interest rate contracts	$ 0	0
Other Liabilities, Fair Value Disclosure		$ 0