Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($) Customer	Mar. 31, 2018 Customer	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Short-term investments	$ 23,000,000			$ 45,500,000
Subscription contracts	The Company’s subscription contracts are generally two years or longer in length, billed annually in advance, and non-cancelable.
ROU assets	$ 13,943,000
Lease, liability	$ 16,371,000
ASU 2016-02 [Member]
ROU assets			$ 14,700,000
Lease, liability			16,900,000
Deferred rent liability reversed to right-of-use asset upon adoption			$ 2,200,000
Incremental and Recoverable Costs
Deferred cost amortization period	4 years
Money Market Funds and U.S. Government Securities
Cash and cash equivalents fair value disclosure	$ 218,500,000
Customer Concentration Risk | Revenue
Number of customers above 10% threshold | Customer	0	0
Customer Concentration Risk | Accounts Receivable
Number of customers above 10% threshold | Customer	0	0
Maximum
Cash and cash equivalent, FDIC insured amount	$ 250,000