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Revenue and Contract Costs - Additional Information (Detail)
 3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Contract assets $ 0 $ 0
Contract with customer, contract duration   1 year
Deferred revenue recognized 45,900,000 $ 103,900,000
Revenue expected to be recognized 246,800,000 246,800,000
Amortization expense related to deferred commissions $ 8,200,000 $ 15,200,000
Minimum [Member]    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Advisory services period   1 hour
Consulting services period   two weeks
Performance obligation, revenue expected to be recognized 12 months 12 months
Maximum [Member]    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Advisory services period   2 days
Consulting services period   three months
Contract with customer, expected payment term   one year
Performance obligation, revenue expected to be recognized 24 months 24 months