Summary of Significant Accounting Policies - Summary of Stock-Based Compensation Expense Recorded in Expense Categories (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	$ 8,490	$ 7,976	$ 8,347
Cost of Services and Fulfillment [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	4,538	4,431	4,573
Selling and Marketing [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	717	1,054	1,152
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total allocated share-based compensation expense	$ 3,235	$ 2,491	$ 2,622