Revenue from Contracts with Customers Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Allowance for Doubtful Accounts Receivable, Current	$ 1,423	$ 1,224	$ 1,678	$ 2,254
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	271	(197)	404
Allowance for Doubtful Accounts Receivable, Write-offs	$ (72)	$ (257)	$ (980)