Property and Equipment, net - Internally Developed Software Costs, Included under Software (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Cost	$ 8,783	$ 2,571
Less : Accumulated amortization	(2,393)	(976)
Net	6,390	1,595
Amortization expense	$ 1,417	$ 640	$ 336