Fair Value Disclosures of Financial Assets - Balances of Assets Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	$ 813,708	$ 907,498
Total assets measured at fair value on a recurring basis	826,298	920,088
Assets Measured at Fair Value on a Nonrecurring Basis	7,109	4,622
Assets Measured at Fair Value on a Nonrecurring Basis	45,900	52,900
Total assets measured at fair value on a nonrecurring basis	52,999	57,526
Collateralized Mortgage Obligation ("CMO") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	125,626	259,396
Federal National Mortgage Association ("FNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	370,654	406,255
Federal Home Loan Mortgage Corporation ("FHLMC") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	109,761	59,650
Government National Mortgage Association ("GNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	108,412	132,455
U.S. Government and agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	43,833	46,990
State and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	55,844	3,209
Reverse Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	(422)	(457)
Trading Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	12,590	12,590
Other real estate owned [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis	7,109	4,622
Impaired loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis	45,890	52,904
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value on a recurring basis
Total assets measured at fair value on a nonrecurring basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Collateralized Mortgage Obligation ("CMO") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Federal National Mortgage Association ("FNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Federal Home Loan Mortgage Corporation ("FHLMC") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Government National Mortgage Association ("GNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | U.S. Government and agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | State and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Reverse Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Trading Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Other real estate owned [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis
Quoted Prices in Active Markets for Identical Asset (Level 1) [Member] | Impaired loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value on a recurring basis	807,753	900,859
Total assets measured at fair value on a nonrecurring basis
Significant Other Observable Inputs (Level 2) [Member] | Collateralized Mortgage Obligation ("CMO") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	119,249	252,300
Significant Other Observable Inputs (Level 2) [Member] | Federal National Mortgage Association ("FNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	370,654	406,255
Significant Other Observable Inputs (Level 2) [Member] | Federal Home Loan Mortgage Corporation ("FHLMC") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	109,761	59,650
Significant Other Observable Inputs (Level 2) [Member] | Government National Mortgage Association ("GNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	108,412	132,455
Significant Other Observable Inputs (Level 2) [Member] | U.S. Government and agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	43,833	46,990
Significant Other Observable Inputs (Level 2) [Member] | State and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	55,844	3,209
Significant Other Observable Inputs (Level 2) [Member] | Reverse Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Other Observable Inputs (Level 2) [Member] | Trading Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Other Observable Inputs (Level 2) [Member] | Other real estate owned [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis
Significant Other Observable Inputs (Level 2) [Member] | Impaired loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets measured at fair value on a recurring basis	18,545	19,229
Total assets measured at fair value on a nonrecurring basis	52,999	57,526
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Mortgage Obligation ("CMO") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	6,377	7,096
Significant Unobservable Inputs (Level 3) [Member] | Federal National Mortgage Association ("FNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Unobservable Inputs (Level 3) [Member] | Federal Home Loan Mortgage Corporation ("FHLMC") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Unobservable Inputs (Level 3) [Member] | Government National Mortgage Association ("GNMA") [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Unobservable Inputs (Level 3) [Member] | U.S. Government and agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Unobservable Inputs (Level 3) [Member] | State and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis
Significant Unobservable Inputs (Level 3) [Member] | Reverse Mortgages [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	(422)	(457)
Significant Unobservable Inputs (Level 3) [Member] | Trading Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Recurring Basis	12,590	12,590
Significant Unobservable Inputs (Level 3) [Member] | Other real estate owned [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis	7,109	4,622
Significant Unobservable Inputs (Level 3) [Member] | Impaired loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets Measured at Fair Value on a Nonrecurring Basis	$ 45,890	$ 52,904