Quarterly report pursuant to Section 13 or 15(d)

Acquisitions - Activity Prior to 2017 (Details)

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Acquisitions - Activity Prior to 2017 (Details) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Business Acquisition [Line Items]      
Gain (loss) recognized due to change in fair value of cash consideration $ (402,000) $ (121,000)  
Acquisitions Prior To 2017      
Business Acquisition [Line Items]      
Total deferred cash obligation 3,800,000   $ 4,400,000
Deferred cash payment amount related to acquisition 600,000 6,700,000  
Aggregate contingent cash obligations 0   $ 200,000
Payments of contingent cash obligations $ 200,000    
Gain (loss) recognized due to change in fair value of cash consideration   $ (200,000)