Revenue Recognition (Contract Balances) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Revenue Recognition
Accounts receivable, net	$ 30,316		$ 33,016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at the beginning of the period	1,529
Provision	8	$ 71
Write-offs	(291)
Balance at the end of the period	$ 1,246
Payment term, general requirement for payment	30 days
Balance at the beginning of the period	$ 8,699
Deferred revenue	4,593
Recognition of deferred revenue	(4,548)
Balance at the end of the period	$ 8,744