Revenue - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
Deferred Revenue [Abstract]
Percentage of subscription in revenue	96.10%	97.60%	97.10%	96.50%
Aggregate revenue under contract			$ 33,910,000
Aggregate revenue recognized			20,564,000
Revenue			$ 18,581,000
Capitalized contract cost amortization period	4 years		4 years
Capitalized commissions	$ 3,056,000		$ 3,056,000		$ 3,110,000
Capitalized additional commissions	595,000		1,092,000
Capitalized commission amortization expense	$ 583,000		$ 1,146,000