Long-Lived Assets - Summary of Aggregate Amortization Related to Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments in client contracts
Finite Lived Intangible Assets [Line Items]
Total amortization expense		$ 7,402	$ 6,591
Capitalized costs
Finite Lived Intangible Assets [Line Items]
Total amortization expense		5,141	2,755
Acquired client contracts
Finite Lived Intangible Assets [Line Items]
Total amortization expense	$ 7,898	5,406	6,683
Total client contracts
Finite Lived Intangible Assets [Line Items]
Total amortization expense	7,898	17,949	16,029
Acquired software
Finite Lived Intangible Assets [Line Items]
Total amortization expense	1,801	1,458	1,806
Internal use software
Finite Lived Intangible Assets [Line Items]
Total amortization expense	9,517	7,845	7,510
Total Software
Finite Lived Intangible Assets [Line Items]
Total amortization expense	$ 11,318	$ 9,303	$ 9,316