Fair Value Measurements - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]
Percent of credit loss	6.40%
Rate of return required	5.00%
Estimated timeframe for auctions of securities minimum	3 years
Estimated timeframe for auctions of securities maximum	5 years
Percentage of liquidity risk premium	5.00%
Increase or decrease in the liquidity risk premium	1.00%
Increase or decrease, respectively, the fair value of the Failed Auction Securities	$ 300,000