Fair Value Measurement - Fair Value, Balance Sheet Grouping (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investment securities:
Held to maturity, at carrying value	$ 399,503	$ 400,248
Mortgage-backed securities:
Held to maturity, at carrying value	260,818	261,339
Level 1
Financial Assets:
Cash and cash equivalents	107,178	84,655
Investment securities:
Held to maturity, at carrying value	0	0
Mortgage-backed securities:
Held to maturity, at carrying value	0	0
FHLB stock and other investments, at cost	0	0
Loans, net of allowance for loan losses	0	0
Loans held for sale	0	0
Financial Liabilities:
Retail deposits	0	0
Federal funds purchased and repurchase agreements	0	0
FHLB advances	0	0
Long-term debt	0	0
Level 2
Financial Assets:
Cash and cash equivalents	0	0
Investment securities:
Held to maturity, at carrying value	399,503	400,248
Mortgage-backed securities:
Held to maturity, at carrying value	260,818	261,339
FHLB stock and other investments, at cost	45,237	43,871
Loans, net of allowance for loan losses	0	0
Loans held for sale	4,096	2,899
Financial Liabilities:
Retail deposits	3,493,430	3,369,784
Federal funds purchased and repurchase agreements	2,127	4,237
FHLB advances	683,933	886,087
Long-term debt	43,844	43,860
Level 3
Financial Assets:
Cash and cash equivalents	0	0
Investment securities:
Held to maturity, at carrying value	0	0
Mortgage-backed securities:
Held to maturity, at carrying value	0	0
FHLB stock and other investments, at cost	0	0
Loans, net of allowance for loan losses	2,129,587	2,140,088
Loans held for sale	0	0
Financial Liabilities:
Retail deposits	0	0
Federal funds purchased and repurchase agreements	0	0
FHLB advances	0	0
Long-term debt	0	0
Carrying Amount
Financial Assets:
Cash and cash equivalents	107,178	84,655
Investment securities:
Held to maturity, at carrying value	388,106	388,823
Mortgage-backed securities:
Held to maturity, at carrying value	249,430	253,496
FHLB stock and other investments, at cost	45,237	43,871
Loans, net of allowance for loan losses	2,157,688	2,167,841
Loans held for sale	4,096	2,899
Financial Liabilities:
Retail deposits	3,495,340	3,374,417
Federal funds purchased and repurchase agreements	2,127	4,237
FHLB advances	690,789	897,420
Long-term debt	60,311	60,311
Estimated Fair Value
Financial Assets:
Cash and cash equivalents	107,178	84,655
Investment securities:
Held to maturity, at carrying value	399,503	400,248
Mortgage-backed securities:
Held to maturity, at carrying value	260,818	261,339
FHLB stock and other investments, at cost	45,237	43,871
Loans, net of allowance for loan losses	2,129,587	2,140,088
Loans held for sale	4,096	2,899
Financial Liabilities:
Retail deposits	3,493,430	3,369,784
Federal funds purchased and repurchase agreements	2,127	4,237
FHLB advances	683,933	886,087
Long-term debt	$ 43,844	$ 43,860

Investment Securities Held-to-maturity Securities, Fair Value Disclosure

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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-Topic 825

-SubTopic 10

-Section 50

-Paragraph 12

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Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

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Fair value portion of short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

No definition available.

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- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(3)(a))

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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=29638263&loc=d3e39828-111592

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

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- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as held-to-maturity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Mortgage-Backed Securities

-URI http://asc.fasb.org/extlink&oid=6517959

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