Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012
Assets:
Fair value measurement disclosure	$ 100,330
U.S. Treasury bills and money market funds
Assets:
Fair value measurement disclosure	97,049
Restricted cash
Assets:
Fair value measurement disclosure	3,281
Fair Value, Inputs, Level 1
Assets:
Fair value measurement disclosure	100,330
Fair Value, Inputs, Level 1 | U.S. Treasury bills and money market funds
Assets:
Fair value measurement disclosure	97,049
Fair Value, Inputs, Level 1 | Restricted cash
Assets:
Fair value measurement disclosure	$ 3,281