Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended
	Oct. 13, 2015	Jul. 22, 2015	Apr. 30, 2015	Jul. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Schedule Of Stockholders Equity [Line Items]
Redeemable convertible preferred stock, outstanding (in shares)					0	0
Additional shares granted to underwriters					1,304,238	1,454,626	1,035,459
Offering expenses							$ 3,097
Common stock, shares issued					44,540,544	43,018,737
Common stock, shares authorized					100,000,000	100,000,000
Common stock warrants, exercised (in shares)						100,000	100,000
Common stock issued upon warrants exercised (in shares)						28,774	53,535
Common stock warrants, outstanding (in shares)					0	0
Term Loan [Member]
Schedule Of Stockholders Equity [Line Items]
Common stock warrants, issued (in shares)								200,000
Logentries [Member]
Schedule Of Stockholders Equity [Line Items]
Number of shares issued as part of acquisition	1,252,627
NT OBJECTives, Inc. [Member]
Schedule Of Stockholders Equity [Line Items]
Number of shares issued as part of acquisition			9,091
IPO [Member]
Schedule Of Stockholders Equity [Line Items]
Conversion of redeemable convertible preferred stock into common stock (in shares)		18,322,605
Number of stock issued (in shares)		7,417,500
Offering price (in dollars per share)		$ 16.00
Additional shares granted to underwriters		967,500
Net proceeds from issuance		$ 107,300
Underwriting discounts and commissions		8,300
Offering expenses		$ 3,100
IPO [Member] | Series D IPO Participation Payment [Member]
Schedule Of Stockholders Equity [Line Items]
Conversion of redeemable convertible preferred stock into common stock (in shares)		1,939,990
IPO and IPO Participation Payment [Member]
Schedule Of Stockholders Equity [Line Items]
Conversion of our preferred stock into common stock, beneficial conversion charge						$ 14,200
Amended and Restated Certificate of Incorporation [Member]
Schedule Of Stockholders Equity [Line Items]
Common stock, shares authorized		100,000,000
Undesignated preferred stock		10,000,000
Technology Crossover Ventures [Member]
Schedule Of Stockholders Equity [Line Items]
Offering price (in dollars per share)		$ 16.00		$ 16.00
Common stock, shares issued		312,500		312,500
Net proceeds from offerings		$ 5,000		$ 5,000
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Number of stock issued (in shares)							7,730,000
Common stock repurchased during period, shares					22,754	62,428
Aggregate amount paid for share repurchase					$ 400	$ 900