Commitments and Contingencies - Additional Information (Detail) (Northern Virginia Office Space, USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012	Oct. 31, 2010 sqft
Northern Virginia Office Space
Commitments and Contingencies [Line Items]
Office space available for lease under the agreement			190,000
Lease expiration date	Dec. 31, 2020
Deferred rent included in other long-term liabilities	$ 22.0	$ 22.7
Deferred rent included in current accrued expenses	$ 2.6	$ 2.5

For a classified balance sheet, the cumulative difference as of the balance sheet date between the payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, within one year of the balance sheet date.

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For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, more than one year after the balance sheet date.

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