Long-Lived Assets - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 87,923	$ 63,136
Less accumulated depreciation and amortization	(40,430)	(27,831)
Property and equipment, net	47,493	35,305
Computer and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,449	1,597
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,317	4,324
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,893	2,148
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,154	5,342
Content
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 70,110	$ 49,725