Revenue Recognition - Additional Information (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Disaggregation Of Revenue [Line Items]
Unbilled receivables related to service	$ 1,200,000	$ 1,200,000
Deferred sales commissions	13,200,000	13,200,000
Amortization expense for the deferred costs	1,300,000	2,600,000
impairment loss related to costs capitalized	0	0
Subscription services revenue recognized from unearned revenue	33,000,000	60,700,000
Subscription Services
Disaggregation Of Revenue [Line Items]
Revenue remaining performance obligation	$ 76,400,000	$ 76,400,000