Disposition of Buyer Platform - Results of Operations for Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses:
Income from discontinued operations, net of income taxes	$ 0	$ 4,516	$ 0	$ 7,198
Loss on sale of discontinued operations, net of income taxes	(161)	0	(136)	0
Total income (loss) from discontinued operations, net of income taxes	(161)	4,516	(136)	7,198
Discontinued operations disposed of by sale | Buyer Platform
Disposition
Revenue	0	38,933	0	74,194
Cost of revenue	0	23,524	0	44,783
Gross profit	0	15,409	0	29,411
Operating expenses:
Technology and development	0	3,081	0	6,317
Sales and marketing	0	6,208	0	12,735
General administrative	0	231	0	441
Depreciation and Amortization	0	1,367	0	2,695
Total operating expenses	0	10,887	0	22,188
Operating income of discontinued operations before income taxes	0	4,522	0	7,223
Provision for income tax on discontinued operations	0	6	0	25
Income from discontinued operations, net of income taxes	0	4,516	0	7,198
Loss on sale of discontinued operations before income taxes	(161)	0	(136)	0
Provision for income taxes on sale of discontinued operations	0	0	0	0
Loss on sale of discontinued operations, net of income taxes	(161)	0	(136)	0
Total income (loss) from discontinued operations, net of income taxes	$ (161)	$ 4,516	$ (136)	$ 7,198