Revenue Recognition (Contract Balances) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenue Recognition
Accounts receivable, net	$ 29,806		$ 29,925
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at the beginning of the period	1,147
Provision	286	$ 264
Write-offs	(104)
Balance at the end of the period	$ 1,329
Payment term, general requirement for payment	30 days
Balance at the beginning of the period	$ 7,682
Deferred revenue	4,266
Recognition of deferred revenue	(3,871)
Balance at the end of the period	8,077
Contracted not recognized revenue	$ 9,500