Summary of Business and Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Incorporation date			Mar. 31, 2006
Allowance for doubtful accounts	$ 2,230,000		$ 2,230,000		$ 2,188,000
Allowance for potential customer credits	1,750,000		1,750,000		2,274,000
Goodwill impairment	0	$ 0	$ 0	$ 0
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Intangible assets amortized useful lives			2 years
Minimum [Member] | Subscription arrangement [Member]
Summary Of Significant Accounting Policies [Line Items]
Length of subscription agreements			1 year
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Intangible assets amortized useful lives			6 years
Money Market Funds [Member] | Level 1 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents - money market funds	$ 22,631,000		$ 22,631,000		$ 25,564,000