Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts receivable, net	$ 38,552	$ 70,023
Deferred commissions	10,884	13,731
Prepaid expenses and other current assets	13,292	18,942
Total current assets	207,180	236,819
Other assets	8,417	6,231
Total assets	328,494	345,200
Deferred revenue	128,435	145,207
Total current liabilities	170,311	195,053
Total liabilities	181,664	204,011
Retained earnings	126,006	123,010
Total stockholders’ equity	146,830	141,189
Total liabilities and stockholders’ equity	328,494	$ 345,200
ASC 606 [Member] | Amounts as if Previous Guidance in Effect [Member]
Accounts receivable, net	41,837
Deferred commissions	10,284
Prepaid expenses and other current assets	17,966
Total current assets	214,539
Other assets	7,855
Total assets	335,291
Deferred revenue	138,060
Total current liabilities	179,936
Total liabilities	191,289
Retained earnings	123,178
Total stockholders’ equity	144,002
Total liabilities and stockholders’ equity	$ 335,291