Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitment And Contingencies [Line Items]
Future rental payments due			$ 90,864,000
Lease exit costs, new office headquarters		200,000
Lease payments for space	500,000		500,000
Tenant allowance total			8,400,000
Rent expense under operating leases			14,100,000	11,400,000	8,800,000
New Lease Arrangement
Commitment And Contingencies [Line Items]
Lease commencement date			Jul. 01, 2011
Lease expiration date			Dec. 31, 2023
Number of additional lease terms			2
Additional lease term (in years)			5
Future rental payments due			$ 75,800,000
Other Lease Arrangements
Commitment And Contingencies [Line Items]
Operating Lease Expiration Year			2020