Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) CreditFacility	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Apr. 01, 2015 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Rent expense	$ 14.3	$ 16.0	$ 14.6
Letter of Credit
Commitments and Contingencies Disclosure [Line Items]
Number of letters of credit issued to secure office space leases (credit facility) | CreditFacility	5
Amount outstanding on letters of credit	$ 4.3	$ 4.6
Cogent Partners, LP
Commitments and Contingencies Disclosure [Line Items]
Contingent consideration, cash				$ 18.9