Long-Lived Assets - Summary of Aggregate Amortization Related to Client Contract Costs (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	$ 6,022	$ 17,285
Client contract incentives
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	2,781	8,272
Capitalized costs
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	2,658	7,495
Capitalized commission fees
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	$ 583	$ 1,518