Long-Lived Assets - Summary of Aggregate Amortization Related to Client Contract Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	$ 23,381
Client contract incentives
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	11,052
Capitalized costs
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	10,304
Capitalized commission fees
Capitalized Contract Cost [Line Items]
Total client contract costs, aggregate amortization	$ 2,025