Accounts Receivable - Activity in Accounts Receivable Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 1,281	$ 925	$ 1,019
Charges to income from operations	3,824	3,407	2,099
Collections from customers previously reserved and other	(3,571)	(3,051)	(2,193)
Ending balance	$ 1,534	$ 1,281	$ 925