Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Lease cancellation notice period	30 days
Commitment maturing in the next fiscal year	$ 78.0
Other commitment, due in second year	93.9
Other commitment, due in third year	$ 43.3
Lease term expiration date	Mar. 31, 2020
Tenant improvement allowance	$ 6.3
Early termination right effective date	Mar. 31, 2018
Early termination fees	$ 1.0
Rent expense	$ 2.1	$ 1.8	$ 1.8