Revenue Recognition - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Unbilled receivables related to service	$ 1,100,000		$ 1,100,000
Deferred sales commissions	17,600,000		17,600,000		$ 16,800,000
Amortization expense for the deferred costs	2,000,000.0	$ 1,300,000	3,600,000	$ 2,600,000
Impairment loss related to costs capitalized			0		$ 0
Subscription Services
Disaggregation Of Revenue [Line Items]
Revenue recognized	35,000,000.0		62,900,000
Revenue remaining performance obligation	$ 200,800,000		$ 200,800,000