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Significant Accounting Policies summary of significant accounting policies narrative (Details) - USD ($)
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Deferred Sales Commission Asset Estimated Period Of Benefit 6 years  
Amortization of Deferred Sales Commissions $ 1,614,000 $ 4,879,000
Other Asset Impairment Charges 0 0
Deferred Sales Commission Expensed When Incurred $ 2,600,000 $ 800,000