Commitments and Contingencies - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) ft²	Jun. 30, 2016 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Rent expense | $	$ 0.8	$ 0.5	$ 1.6	$ 1.0
Washington DC Lease
Commitments and Contingencies Disclosure [Line Items]
Leased square footage			40,188
Expiration date of leases for office space			2026
Washington DC Lease | Sublease
Commitments and Contingencies Disclosure [Line Items]
Leased square footage			9,928
Washington DC Lease Amendment
Commitments and Contingencies Disclosure [Line Items]
Leased square footage			30,260
Renewal term of lease agreement			5 years
London Lease
Commitments and Contingencies Disclosure [Line Items]
Leased square footage			2,880
Noncancellable lease term ending date			2021
Berlin Lease
Commitments and Contingencies Disclosure [Line Items]
Leased square footage			1,249