Revenue - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Deferred revenue expect to recognize amount	$ 3.9
Deferred revenue expect to recognize period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Deferred revenue expect to recognize amount	$ 7.9
Deferred revenue expect to recognize period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue practical expedient remaining performance obligation description	We have elected to apply the practical expedient not to disclose the value of unsatisfied performance obligations for contracts that are less than one year in length. However, this expedient cannot be applied to initial 30-day contracts with a client that also contain an implied performance obligation in the form of a material right as the material right performance obligation is being recognized over the expected client life which exceeds one year
Revenue practical expedient performance obligation estimated client life	10 years
Deferred revenue expect to recognize amount	$ 45.4
Deferred revenue expect to recognize description	We expect to recognize $3.9 million of deferred revenue related to material right performance obligations in 2018, $7.9 million of such deferred revenue in 2019, and $45.4 million of such deferred revenue thereafter