Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	$ (2,833)	$ (3,388)	$ (1,619)
Provision for doubtful accounts	1,713	1,515	3,111
Write-off of accounts receivable against allowance	(428)	(2,258)	(1,342)
Other	25	188	0
Ending balance	(4,143)	(2,833)	(3,388)
Valuation Allowance, Operating Loss Carryforwards [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balance	(3,747)	(5,979)	0
Valuation Allowances and Reserves, Period Increase (Decrease)	3,712	2,232	(5,979)
Ending balance	$ (35)	$ (3,747)	$ (5,979)