Description of Operations and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Description Of Operations And Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ (204,964)	$ (196,865)
Service contracts
Description Of Operations And Summary Of Significant Accounting Policies [Line Items]
Contracts amortization period	1 year
Minimum | Subscription contracts
Description Of Operations And Summary Of Significant Accounting Policies [Line Items]
Contracts amortization period	1 year
Maximum | Subscription contracts
Description Of Operations And Summary Of Significant Accounting Policies [Line Items]
Contracts amortization period	4 years