Summary of Significant Accounting Policies - Subscription Revenue - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016
Short Term [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Subscription contract period	3 months
Short Term [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Subscription contract period	12 months
Long Term [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Subscription contract period	1 year
Long Term [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Subscription contract period	3 years