Quarterly report pursuant to Section 13 or 15(d)

Acquisitions - Activity Prior to 2016 (Details)

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Acquisitions - Activity Prior to 2016 (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Business Acquisition [Line Items]          
Gain (loss) recognized due to change in fair value of cash consideration     $ (382,000) $ 499,000  
Acquisitions Prior to 2016          
Business Acquisition [Line Items]          
Total deferred cash obligation $ 100,000   100,000   $ 6,600,000
Deferred cash payment amount related to acquisition     6,400,000 5,100,000  
Aggregate contingent cash obligations 0   0   $ 2,000
Payments of contingent cash obligations     700,000    
Gain (loss) recognized due to change in fair value of cash consideration $ 700,000 $ 400,000 $ (700,000) $ 800,000