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 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Business Acquisition [Line Items]          
Gain (loss) recognized due to change in fair value of cash consideration     $ (1,124,000) $ (1,024,000)  
Acquisitions Prior To 2017          
Business Acquisition [Line Items]          
Total deferred cash obligation $ 2,700,000   2,700,000   $ 4,400,000
Deferred cash payment amount related to acquisition     1,800,000 7,000,000  
Payments of contingent cash obligations     200,000 500,000  
Aggregate contingent cash obligations 0   0   $ 200,000
Gain (loss) recognized due to change in fair value of cash consideration   $ (100,000) (100,000) $ (200,000)  
2017 Acquisitions          
Business Acquisition [Line Items]          
Deferred cash payment amount related to acquisition     $ 6,000,000    
Gain (loss) recognized due to change in fair value of cash consideration $ 100,000 $ 200,000