Fair Value Measurement - Quantitative Information About Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 594
Valuation Technique	Discounted cash flow
Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	637	6,166
Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	1,564	3,489
Permanent Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	2,315	3,172
Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	4,125	6,918
Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value		$ 257
Sales Comparison Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique	Sales comparison approach	Sales comparison approach
Sales Comparison Approach [Member] | Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique	Sales comparison approach	Sales comparison approach
Sales Comparison Approach [Member] | Permanent Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique	Sales comparison approach	Sales comparison approach
Sales Comparison Approach [Member] | Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique	Sales comparison approach	Sales comparison approach
Sales Comparison Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique		Sales comparison approach
Income Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique	Income approach	Income approach
Income Approach [Member] | Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique		Income approach
Income Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Valuation Technique		Income approach
Weighted Average [Member] | Sales Comparison Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	11.78%	28.75%
Weighted Average [Member] | Sales Comparison Approach [Member] | Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	11.90%	9.83%
Weighted Average [Member] | Sales Comparison Approach [Member] | Permanent Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	17.76%	10.20%
Weighted Average [Member] | Sales Comparison Approach [Member] | Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	9.24%	17.63%
Weighted Average [Member] | Sales Comparison Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales		11.15%
Weighted Average [Member] | Income Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences in net operating income Capitalization rate	9.41%	9.49%
Weighted Average [Member] | Income Approach [Member] | Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences in net operating income Capitalization rate		10.00%
Weighted Average [Member] | Income Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences in net operating income Capitalization rate		9.25%
Minimum [Member] | Sales Comparison Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	0.00%	12.07%
Minimum [Member] | Sales Comparison Approach [Member] | Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	0.00%	0.00%
Minimum [Member] | Sales Comparison Approach [Member] | Permanent Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	6.00%	3.60%
Minimum [Member] | Sales Comparison Approach [Member] | Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	6.54%	0.00%
Minimum [Member] | Sales Comparison Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales		1.60%
Minimum [Member] | Income Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	3.95%	7.52%
Minimum [Member] | Income Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales		8.50%
Maximum [Member] | Sales Comparison Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	56.90%	45.44%
Maximum [Member] | Sales Comparison Approach [Member] | Impaired Loans Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	25.00%	25.00%
Maximum [Member] | Sales Comparison Approach [Member] | Permanent Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	46.53%	16.47%
Maximum [Member] | Sales Comparison Approach [Member] | Construction [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	26.63%	47.24%
Maximum [Member] | Sales Comparison Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales		24.18%
Maximum [Member] | Income Approach [Member] | Impaired Loans Permanent Real Estate Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales	14.62%	10.73%
Maximum [Member] | Income Approach [Member] | Commercial Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Adjustment for differences between comparable sales		10.00%