Fair Value Measurements and Disclosures - Assets Measured at Fair Value on Non-Recurring Basis of Impairment Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measured on non-recurring basis, impaired loans	$ 10,610	$ 18,831	$ 16,030
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measured on non-recurring basis, impaired loans	$ 10,610	$ 18,831	$ 16,030