Schedule II Valuation Accounts (Details) - Allowance For Doubtful Accounts [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 1,340	$ 548	$ 680
Net Additions to Expense		402	3,151	448
Deductions	[1]	(302)	(2,359)	(580)
Balance at End of Period		$ 1,440	$ 1,340	$ 548

[1] Primarily consists of write-offs, net of recoveries and other adjustments