Annual report pursuant to Section 13 and 15(d)

Acquisitions - Acquisitions Prior to 2014 (Details)

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Acquisitions - Acquisitions Prior to 2014 (Details) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Business Acquisition [Line Items]      
Gain (loss) due to changes in contingent cash payments $ (877,000) $ (3,268,000) $ 173,000
Acquisitions Prior to 2014      
Business Acquisition [Line Items]      
Deferred cash obligation 100,000 1,000,000  
Paid deferred cash obligations 900,000 1,400,000  
Liability for the estimated cash payment $ 0 0  
Paid contingent cash obligations   700,000  
Gain (loss) due to changes in contingent cash payments   $ 1,100,000