Intangible Assets - Schedule of Amortization Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Total amortization	$ 3,862	$ 4,041	$ 4,134
Acquired technology and domain name
Finite-Lived Intangible Assets [Line Items]
Total amortization	3,035	3,041	3,047
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Total amortization	500	673	760
Trade names
Finite-Lived Intangible Assets [Line Items]
Total amortization	$ 327	$ 327	$ 327