Revenues - Components of Deferred Revenue and Customer Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Deferred Revenue and Customer Liabilities [Line Items]
Deferred revenue and customer liabilities	$ 27,077	$ 30,176
Deferred Revenue and Customer Liabilities [Member]
Schedule of Deferred Revenue and Customer Liabilities [Line Items]
Deferred revenue	3,381	3,655
Customer arrangements with termination rights	15,992	16,404
Estimated refund liabilities	$ 7,704	$ 10,117