Quarterly report pursuant to Section 13 or 15(d)

Long-Term Incentive Plan (Details)

v3.7.0.1
Long-Term Incentive Plan (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Apr. 17, 2017
2017 LTIP      
Aggregate disclosure      
Number of common shares may be delivered pursuant to awards, subject to customary adjustments     930,851
Awards granted 0    
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 99,500 99,500  
Outstanding units 99,500 99,500  
Threshold limit for quarterly distribution   $ 7.5  
Threshold limit for conversion of units to common shares $ 2,000.0 $ 2,000.0  
Assumptions:      
Vesting period   3 years  
Aggregate disclosure      
Expense recognized 9.6 $ 18.0  
Unamortized compensation expense related to nonvested Series B units 89.8 $ 89.8  
Weighted average period for recognizing unrecognized stock-based compensation expense   2 years 6 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  
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 $ 7.5 $ 15.3  
Awards granted   92,000  
Awards forfeited 500    
IDR LLC | Series B Unit Awards classified as liability      
Assumptions:      
Floor equity value $ 4,100.0 $ 4,100.0  
Expected volatility (as a percent)   42.00%  
Risk free rate (as a percent)   2.28%  
Weighted average cost of capital (as a percent)   7.25%  
Estimated value (in dollars per unit)   $ 2,042  
Aggregate disclosure      
Expense recognized $ 2.1 $ 2.7  
Awards granted   8,000