Fair Value Measurements - Financial Assets and Financial Liabilities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	$ 208,861
Mortgage-backed securities available for sale	383,134	333,857
Items Measured on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities available for sale	383,134	333,857
Items Measured on a Recurring Basis [Member] | U.S. Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	138,885	139,050
Items Measured on a Recurring Basis [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	24,889	25,780
Items Measured on a Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	45,087	43,470
Items Measured on a Recurring Basis [Member] | Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	5,685	5,293
Items Measured on a Non-Recurring Basis [Member] | Other Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,813	3,210
Items Measured on a Non-Recurring Basis [Member] | Loans Measured for Impairment Based on the Fair Value of Underlying Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	12,497	12,033
Level 1 Inputs [Member] | Items Measured on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities available for sale
Level 1 Inputs [Member] | Items Measured on a Recurring Basis [Member] | U.S. Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 1 Inputs [Member] | Items Measured on a Recurring Basis [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 1 Inputs [Member] | Items Measured on a Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 1 Inputs [Member] | Items Measured on a Recurring Basis [Member] | Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	5,685	5,293
Level 1 Inputs [Member] | Items Measured on a Non-Recurring Basis [Member] | Other Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value
Level 1 Inputs [Member] | Items Measured on a Non-Recurring Basis [Member] | Loans Measured for Impairment Based on the Fair Value of Underlying Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value
Level 2 Inputs [Member] | Items Measured on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities available for sale	383,134	333,857
Level 2 Inputs [Member] | Items Measured on a Recurring Basis [Member] | U.S. Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	138,885	139,050
Level 2 Inputs [Member] | Items Measured on a Recurring Basis [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	24,889	25,780
Level 2 Inputs [Member] | Items Measured on a Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale	45,087	43,470
Level 2 Inputs [Member] | Items Measured on a Recurring Basis [Member] | Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 2 Inputs [Member] | Items Measured on a Non-Recurring Basis [Member] | Other Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value
Level 2 Inputs [Member] | Items Measured on a Non-Recurring Basis [Member] | Loans Measured for Impairment Based on the Fair Value of Underlying Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value
Level 3 Inputs [Member] | Items Measured on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities available for sale
Level 3 Inputs [Member] | Items Measured on a Recurring Basis [Member] | U.S. Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 3 Inputs [Member] | Items Measured on a Recurring Basis [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 3 Inputs [Member] | Items Measured on a Recurring Basis [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 3 Inputs [Member] | Items Measured on a Recurring Basis [Member] | Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available for sale
Level 3 Inputs [Member] | Items Measured on a Non-Recurring Basis [Member] | Other Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,813	3,210
Level 3 Inputs [Member] | Items Measured on a Non-Recurring Basis [Member] | Loans Measured for Impairment Based on the Fair Value of Underlying Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 12,497	$ 12,033