Long-Lived Assets - Summary of Carrying Values of Contract Cost Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Gross Carrying Amount	$ 72,622
Accumulated Amortization	(37,038)	$ 0
Net Amount	35,584
Client contract incentives
Capitalized Contract Cost [Line Items]
Gross Carrying Amount	28,366
Accumulated Amortization	(18,053)
Net Amount	10,313
Capitalized costs
Capitalized Contract Cost [Line Items]
Gross Carrying Amount	37,313
Accumulated Amortization	(17,485)
Net Amount	19,828
Capitalized commission fees
Capitalized Contract Cost [Line Items]
Gross Carrying Amount	6,943
Accumulated Amortization	(1,500)
Net Amount	$ 5,443