Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 1,037	$ 226	$ 185
Charged to Bad Debt Expense		(235)	916	107
Charged to Other Accounts		0	0	0
Deductions	[1]	(332)	(105)	(66)
Balance at End of Period		$ 470	$ 1,037	$ 226

[1] Deductions represent the actual write-off of accounts receivable balances.