Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Assets:
Fair value measurement disclosure	$ 21,595
U.S. Treasury bills and money market funds
Assets:
Fair value measurement disclosure	18,049
Restricted cash
Assets:
Fair value measurement disclosure	3,546
Fair Value, Inputs, Level 1
Assets:
Fair value measurement disclosure	21,595
Fair Value, Inputs, Level 1 | U.S. Treasury bills and money market funds
Assets:
Fair value measurement disclosure	18,049
Fair Value, Inputs, Level 1 | Restricted cash
Assets:
Fair value measurement disclosure	$ 3,546