Summary of Significant Accounting Policies - Trade Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts, beginning balance	$ 1,949	$ 1,490	$ 1,517
Charged to costs and expenses	3,767	1,407	1,601
Amounts charged off, net	(1,345)	(948)	(1,628)
Allowance for doubtful accounts, ending balance	$ 4,371	$ 1,949	$ 1,490