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Fair Value Measurements - Additional Information (Detail)
 9 Months Ended
Sep. 30, 2015
USD ($)
Fair Value Disclosures [Abstract]  
Percent of credit loss 2.40%
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 $ 100,000
Fair value transfers between Level 1 and Level 2 $ 0