Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $) In Thousands, unless otherwise specified			9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member]	Sep. 30, 2014 Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Earning Maximum Rate Until Maturity [Member]	Sep. 30, 2014 Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Principal Return Prior to Maturity [Member]	Sep. 30, 2014 Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Default [Member]	Sep. 30, 2014 Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Liquidity Risk Premium [Member]	Sep. 30, 2014 Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Recovery Rate in Default [Member]	Sep. 30, 2014 Minimum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Earning Maximum Rate Until Maturity [Member]	Sep. 30, 2014 Minimum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Principal Return Prior to Maturity [Member]	Sep. 30, 2014 Minimum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Default [Member]	Sep. 30, 2014 Minimum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Liquidity Risk Premium [Member]	Sep. 30, 2014 Minimum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Recovery Rate in Default [Member]	Sep. 30, 2014 Maximum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Earning Maximum Rate Until Maturity [Member]	Sep. 30, 2014 Maximum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Principal Return Prior to Maturity [Member]	Sep. 30, 2014 Maximum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Cumulative Probability of Default [Member]	Sep. 30, 2014 Maximum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Liquidity Risk Premium [Member]	Sep. 30, 2014 Maximum [Member] Failed Auction Securities [Member] Significant Unobservable Inputs (Level 3) [Member] Recovery Rate in Default [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 5,675	$ 5,651	$ 4,964
Valuation Technique			Discounted cash flow
Unobservable Input				Cumulative probability of earning the maximum rate until maturity	Cumulative probability of principal return prior to maturity	Cumulative probability of default	Liquidity risk premium	Recovery rate in default
Weighted Average Interest Rate				0.04%	84.10%	15.86%	5.00%	40.00%	0.01%	73.05%	4.84%	5.00%	40.00%	0.07%	95.15%	26.88%	5.00%	40.00%