Revenue Recognition - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Receivables related to service	$ 1,600,000		$ 1,600,000
Deferred sales commissions current	7,700,000		7,700,000		$ 6,500,000
Deferred sales commissions noncurrent	12,000,000.0		12,000,000.0		10,300,000
Amortization expense for the deferred costs	1,900,000	$ 1,400,000	5,500,000	$ 3,900,000
Impairment loss related to costs capitalized	0		0		$ 0
Subscription Services
Disaggregation Of Revenue [Line Items]
Revenue recognized	36,900,000		77,000,000.0
Revenue remaining performance obligation	250,900,000		250,900,000
Professional Services
Disaggregation Of Revenue [Line Items]
Revenue recognized	4,100,000		5,200,000
Revenue remaining performance obligation	$ 12,200,000		$ 12,200,000