Commitments and Contingencies - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended			1 Months Ended			12 Months Ended
	Oct. 31, 2011	Jan. 02, 2009	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jul. 15, 2009 Initial Shares [Member]	Jul. 15, 2009 Earnout Shares [Member]	Dec. 31, 2012 Class A Common stock [Member]	Dec. 31, 2013 Subsequent event [Member]	Dec. 31, 2012 Buildings [Member]	Dec. 31, 2011 Buildings [Member]
Contingencies And Commitments [Line Items]
Office space under agreement, expires through			2033
Rental expense relating to operating leases			$ 80,888	$ 76,718	$ 66,350
Sublease income			9,613	10,967	10,478
Capital lease obligation payable through			2017
Weighted average interest rate of capital			6.30%
Obligations collateralized by certain assets with a net book value										21,932	22,491
Book value of assets under capital lease			23,486	24,589
Liabilities of abandoned leased facilities in the U.K.			7,516	10,632
Charge on abandoned lease facilities				5,539
Guarantees indemnifications			5,028
Collateral/counter-guarantees			3,890
Payment for equity interests in LAM	90,000	60,000
Issue of class A common stock	2,210,520
Withheld shares for tax obligations in lieu of delivery of shares	68,384
Additional cash payment subject to delayed payment/issuance until eighth anniversary			961
Additional issuance of class A common shares subject to delayed issuance until eighth anniversary			24,537
Aggregate fair value of consideration recognized by the company at acquisition date and			61,624
Initial shares issued at acquisition						1,142,857
Additional shares issued and subject to earnout criteria and payable over time							1,142,857
Earnout shares earned			1,209,154	514,850
Earnout shares became settled			686,004	343,002
Maximum earn-out consideration payable over all years			7,000	7,000					7,000
Common stock issuable on contingent basis								121,076
Other commitments			$ 23,000