Quarterly report pursuant to Section 13 or 15(d)

Income Taxes - Narrative (Details)

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Income Taxes - Narrative (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Income Tax Contingency [Line Items]            
Income tax provision (benefit)   $ 22,923,000 $ (923,000) $ 5,523,000 $ (650,000)  
Effective tax rate (as a percent)   37.00%   7.00%    
Operating loss carryforwards   $ 33,400,000   $ 33,400,000    
Valuation allowance   2,900,000   $ 2,900,000    
Tax Receivable Agreement | Tema            
Income Tax Contingency [Line Items]            
Deferred tax assets $ 5,700,000         $ 5,700,000
Increase (decrease) of valuation allowance $ 200,000         $ (1,500,000)
Payment of net cash savings (as a percent)       90.00%    
Estimated deferred tax liabilities   50,400,000   $ 50,400,000    
Deferred tax liabilities   $ 0   $ 0    
Payment of estimated future cash tax savings (as a percent)       90.00%