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Summary of Fair Value Transfers Between Level I and Level II (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2015
Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Transfers from Level I into Level II [1] $ 287 $ 287  
Transfers from Level II into Level I [2] $ 26,534 $ 32,312 $ 67,327
[1] Transfers out of Level I represent those financial instruments for which restrictions exist and adjustments were made to an otherwise observable price to reflect fair value at the reporting date.
[2] Transfers into Level I represent those financial instruments for which an unadjusted quoted price in an active market became available for the identical asset.