Stockholders' Equity - Summary of Stock-Based Compensation Recorded in Expense Categories (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	$ 3,072	$ 2,120	$ 8,605	$ 6,191
Cost of Services and Fulfillment [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	1,782	1,001	4,812	3,128
Selling and Marketing [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	441	261	1,366	752
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	$ 849	$ 858	$ 2,427	$ 2,311