Fair Value Accounting and Measurement Fair Value Accounting and Measurement (Carrying Amounts and Estimated Fair Values of Selected Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets
Interest-earning deposits with banks	$ 16,949	$ 14,531
Securities available for sale	2,098,257	1,664,111
Reported Value Measurement [Member]
Assets
Cash and due from banks	171,221	165,030
Interest-earning deposits with banks	16,949	14,531
Securities available for sale	2,098,257	1,664,111
FHLB stock	33,365	32,529
Loans held for sale	1,116	735
Loans	5,375,809	4,444,842
FDIC loss-sharing asset	15,174	39,846
Interest rate contracts	11,800	9,044
Liabilities
Deposits	6,924,722	5,959,475
FHLB Advances	216,568	36,606
Repurchase agreements	105,080	25,000
Other borrowings	8,248
Interest rate contracts	11,851	9,044
Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	171,221	165,030
Interest-earning deposits with banks	16,949	14,531
Securities available for sale	2,098,257	1,664,111
FHLB stock	33,365	32,529
Loans held for sale	1,116	735
Loans	5,516,286	4,605,038
FDIC loss-sharing asset	4,054	11,248
Interest rate contracts	11,800	9,044
Liabilities
Deposits	6,921,804	5,958,747
FHLB Advances	217,296	35,080
Repurchase agreements	106,171	26,361
Other borrowings	8,248
Interest rate contracts	11,851	9,044
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Assets
Cash and due from banks	171,221	165,030
Interest-earning deposits with banks	16,949	14,531
Securities available for sale	20,499	20,114
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	6,416,017	5,449,546
FHLB Advances	0	0
Repurchase agreements	0	0
Other borrowings	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
Securities available for sale	2,077,758	1,643,997
FHLB stock	33,365	32,529
Loans held for sale	1,116	735
Loans	0	0
FDIC loss-sharing asset	0	0
Interest rate contracts	11,800	9,044
Liabilities
Deposits	505,787	509,201
FHLB Advances	217,296	35,080
Repurchase agreements	106,171	26,361
Other borrowings	8,248
Interest rate contracts	11,851	9,044
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
Securities available for sale	0	0
FHLB stock	0	0
Loans held for sale	0	0
Loans	5,516,286	4,605,038
FDIC loss-sharing asset	4,054	11,248
Interest rate contracts	0	0
Liabilities
Deposits	0	0
FHLB Advances	0	0
Repurchase agreements	0	0
Other borrowings	0
Interest rate contracts	$ 0	$ 0