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Schedule II - Valuation and Qualifying Accounts - Summary of 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]      
Balance at Beginning of Period $ 1,385 $ 1,299 $ 1,348
Additions Charged to Costs and Expenses 641 369 506
Additions Charged to Other Accounts
Deductions (416) (283) (555)
Balance at End of Period 1,610 1,385 1,299
Valuation Allowance of Deferred Tax Assets [Member]      
Balance at Beginning of Period 2,017 1,030 1,381
Additions Charged to Costs and Expenses 362 987
Additions Charged to Other Accounts
Deductions (351)
Balance at End of Period $ 2,379 $ 2,017 $ 1,030