Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) Customer	Jun. 30, 2017 Customer	Jun. 30, 2018 USD ($) Customer	Jun. 30, 2017 Customer	Dec. 31, 2017 Customer	Jan. 01, 2018 USD ($)
Revenue, Major Customer [Line Items]
Period to complete Professional service arrangements			90 days
Deferred costs amortization period			5 years
Customer deposits	$ 2,600,000		$ 2,600,000
Services revenue recognized	36,100,000		82,500,000
Capitalized incremental contract origination costs included in deferred costs	23,706		23,706			$ 15,911
Amortization costs	1,270		2,311
Impairments of deferred costs	$ 0		$ 0
Minimum [Member]
Revenue, Major Customer [Line Items]
Standard payment terms to customers range			30 days
Maximum [Member]
Revenue, Major Customer [Line Items]
Deferred costs expected benefit period			1 year
Standard payment terms to customers range			90 days
Subscription Services [Member] | Minimum [Member]
Revenue, Major Customer [Line Items]
Performance obligation service revenue satisfaction period	1 year		1 year
Subscription Services [Member] | Maximum [Member]
Revenue, Major Customer [Line Items]
Performance obligation service revenue satisfaction period	3 years		3 years
Maintenance and Support Services [Member] | Minimum [Member]
Revenue, Major Customer [Line Items]
Performance obligation service revenue satisfaction period	1 year		1 year
Maintenance and Support Services [Member] | Maximum [Member]
Revenue, Major Customer [Line Items]
Performance obligation service revenue satisfaction period	3 years		3 years
Credit Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Number of customers representing 10% or more of gross accounts receivable | Customer	2		2		1
Number of customers representing 18% or more of gross accounts receivable | Customer					1
Revenue [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Number of customers representing 10% or more of revenue | Customer	0	1	0	1
Minimum percentage of revenue or gross accounts receivable balance		12.00%		12.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Minimum percentage of revenue or gross accounts receivable balance					18.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Customer One [Member]
Revenue, Major Customer [Line Items]
Minimum percentage of revenue or gross accounts receivable balance			12.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Customer Two [Member]
Revenue, Major Customer [Line Items]
Minimum percentage of revenue or gross accounts receivable balance			10.00%