Quarterly report pursuant to Section 13 or 15(d)

Non-Controlling Interests (Details)

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Non-Controlling Interests (Details) - USD ($)
$ in Thousands
3 Months Ended
Jun. 30, 2017
Sep. 30, 2015
Sep. 30, 2018
Dec. 31, 2017
Noncontrolling Interest [Abstract]        
Term of extension of call option 6 months 6 months    
Term of extension of put option 1 year 1 year    
Variable Interest Entity [Line Items]        
Redeemable non-controlling interests     $ 14,585 $ 10,338
Minimum        
Variable Interest Entity [Line Items]        
Exercise price of put options $ 544      
Maximum        
Variable Interest Entity [Line Items]        
Exercise price of put options $ 917