Long-Lived Assets - Summary of Aggregate Amortization Related to Client Contract Costs (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	$ 5,785	$ 11,263
Client contract incentives
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	2,764	5,491
Capitalized costs
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	2,442	4,837
Capitalized commission fees
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	$ 579	$ 935