Commitments and Contingencies - Additional Information (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Jul. 15, 2009	Jun. 30, 2015	Mar. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012
Other Commitments [Line Items]
Office space and equipment under non-cancelable lease agreements, expiration through year				2033
Rental expense relating to operating leases				$ 76,704,000	$ 79,549,000	$ 80,773,000
Office space under sublease agreements, expiration through year				2022
Sublease income				$ 7,858,000	9,587,000	11,751,000
Capital lease obligation payable through				2017
Weighted average interest rate of capital				6.10%
Book value of assets under capital lease				$ 13,628,000	15,273,000
Abandoned leased space (principally in the U.K.)				4,973,000	$ 8,760,000
Guarantees indemnifications				3,340,000
Collateral/counter-guarantees				3,259,000
LFB [Member]
Other Commitments [Line Items]
Other commitments				0
LFNY [Member]
Other Commitments [Line Items]
Other commitments				$ 0
Edgewater Acquisition [Member]
Other Commitments [Line Items]
Aggregate fair value of consideration recognized by the company at acquisition date	$ 61,624,000
Common stock issued and issuable	1,142,857
Additional shares of Class A common stock subject to earnout criteria and payable over time	1,142,857
Initial and Earnout shares earned and settled				2,285,714	1,371,992
Contingent shares issued upon satisfaction of performance thresholds				913,722
Noncash tax benefit recorded in deferred tax assets as result of the delivery of contingent shares				$ 12,000,000
Other Business Acquisitions [Member]
Other Commitments [Line Items]
Common stock issued and issuable			170,988
Number of contingent additional shares earned				0
Common stock issuable on non-contingent basis							170,988
Shares issued due to achievement of certain performance thresholds		27,316
Other Business Acquisitions [Member] | Class A Common Stock [Member]
Other Commitments [Line Items]
Common stock issued and issuable				60,817
Other Business Acquisitions [Member] | Class A Common Stock [Member] | Non-Contingent [Member]
Other Commitments [Line Items]
Common stock issued and issuable				206,612
Other Business Acquisitions [Member] | Class A Common Stock [Member] | Maximum [Member]
Other Commitments [Line Items]
Contingent shares issuable upon satisfaction of performance thresholds				816,492
U.K Lease [Member]
Other Commitments [Line Items]
Abandoned leased space (principally in the U.K.)				$ 2,819,000	$ 6,155,000
Buildings [Member]
Other Commitments [Line Items]
Net book value of certain buildings that primarily collateralized capital lease obligations				$ 13,538,000	15,121,000
LMDC Holdings [Member]
Other Commitments [Line Items]
Sublease income					$ 1,281,000	$ 3,097,000