Quarterly report pursuant to Section 13 or 15(d)

Long-Term Incentive Plan (Details)

v3.8.0.1
Long-Term Incentive Plan (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 5 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2017
Sep. 30, 2017
Apr. 17, 2017
2017 LTIP        
Aggregate disclosure        
Expense recognized   $ 0.1    
Number of common shares may be delivered pursuant to awards, subject to customary adjustments       930,851
Awards granted   3,850    
Remaining shares granted 927,001 927,001 927,001  
IDR LLC        
Long-Term Incentive Plan        
Percentage of amount of quarterly distribution in excess of threshold limit     6.00%  
Threshold limit for quarterly distribution     $ 7.5  
IDR LLC | Series B unit awards        
Long-Term Incentive Plan        
Authorized units 98,600 98,600 98,600  
Outstanding units 98,600 98,600 98,600  
Threshold limit for quarterly distribution     $ 7.5  
Threshold limit for conversion of units to common shares $ 2,000.0 $ 2,000.0 $ 2,000.0  
Assumptions:        
Vesting period     3 years  
Aggregate disclosure        
Expense recognized 8.2   $ 26.2  
Unamortized compensation expense related to nonvested Series B units 78.6 78.6 $ 78.6  
Weighted average period for recognizing unrecognized stock-based compensation expense     2 years 3 months  
IDR LLC | Series B unit awards | Maximum        
Long-Term Incentive Plan        
Percentage of amount of quarterly distribution in excess of threshold limit     6.00%  
Percentage of amount of equity value in excess of threshold limit for conversion of units to common shares     6.00%  
Percentage of newly issued common shares to the total number of issued and outstanding common shares allowed     6.00%  
IDR LLC | Series B Unit Awards classified as equity        
Assumptions:        
Floor equity value 2,000.0 2,000.0 $ 2,000.0  
Expected volatility (as a percent)     43.00%  
Risk free rate (as a percent)     2.45%  
Weighted average cost of capital (as a percent)     7.25%  
Estimated value (in dollars per unit)     $ 999  
Aggregate disclosure        
Expense recognized 7.6   $ 22.9  
Awards granted     92,000  
Awards forfeited     500  
IDR LLC | Series B Unit Awards classified as liability        
Assumptions:        
Floor equity value 4,000.0 $ 4,000.0 $ 4,000.0  
Expected volatility (as a percent)     41.00%  
Risk free rate (as a percent)     2.28%  
Weighted average cost of capital (as a percent)     7.25%  
Estimated value (in dollars per unit)     $ 1,884  
Aggregate disclosure        
Expense recognized $ 0.6   $ 3.3  
Awards granted     8,000  
Awards forfeited     900