Property, Equipment and Software, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, equipment and software, at cost	$ 58,539	$ 55,485
Less accumulated depreciation and amortization	(34,967)	(26,080)
Property, equipment and software, net	$ 23,572	29,405
Computer/office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	36 months
Property, equipment and software, at cost	$ 15,419	15,671
Capitalized internal-use software
Property, Plant and Equipment [Line Items]
Estimated Useful Life	36 months
Property, equipment and software, at cost	$ 24,784	21,789
Amortization expense	4,900	4,200	$ 2,800
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software, at cost	$ 18,336	$ 18,025