Loans and Allowance for Loan Losses, Based on Impairment Review Method (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	$ 0	$ 0
Collectively evaluated for impairment	45,944	46,327
Total ending allowance balance	45,944	46,327	47,035	47,714
Loans [Abstract]
Individually evaluated for impairment	25,724	26,535
Collectively evaluated for impairment	3,167,901	3,131,797
Total loans	3,193,625	3,158,332
Commercial [Member]
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	4,024	4,071
Total ending allowance balance	4,024	4,071	3,840	4,019
Loans [Abstract]
Individually evaluated for impairment	2,780	4,129
Collectively evaluated for impairment	209,365	219,253
Total loans	212,145	223,382
1 to 4 Family Residential Real Estate [Member]
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	41,529	42,088
Total ending allowance balance	41,529	42,088	43,091	43,597
Loans [Abstract]
Individually evaluated for impairment	22,944	22,406
Collectively evaluated for impairment	2,950,533	2,904,950
Total loans	2,973,477	2,927,356
Installment [Member]
Ending allowance balance attributable to loans [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	391	168
Total ending allowance balance	391	168	104	98
Loans [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	8,003	7,594
Total loans	$ 8,003	$ 7,594

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 50

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

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-Publisher FASB

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-Topic 310

-SubTopic 10

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-Paragraph 11B

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The balance of financing receivables that were individually evaluated for impairment.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

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-Paragraph 11B

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-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

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-Article 9

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-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section L

-Subsection 1

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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