Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities - Narrative (Details)

v3.10.0.1
Derivative Instruments and Hedging Activities - Narrative (Details)
$ in Thousands
 1 Months Ended 3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
contract
Apr. 30, 2018
MMBTU
$ / MMBTU
Mar. 31, 2018
MMBTU
$ / MMBTU
Feb. 28, 2018
USD ($)
Mar. 31, 2010
Jun. 30, 2018
USD ($)
contract
Jun. 30, 2017
USD ($)
Jun. 30, 2014
USD ($)
Jun. 30, 2018
USD ($)
contract
Jun. 30, 2017
USD ($)
Dec. 31, 2017
contract
Mar. 31, 2011
USD ($)
Derivative [Line Items]                        
Other expenses, net | $           $ (3,966) $ (1,738)   $ (7,510) $ (3,564)    
Not Designated as Hedging Instrument                        
Derivative [Line Items]                        
Number of instruments held | contract 5         5     5   1  
Interest rate swap instruments | Reclassification out of Accumulated Other Comprehensive Income | Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest                        
Derivative [Line Items]                        
Other expenses, net | $               $ 566 $ (34)      
Interest rate swap instruments | Derivatives Designated as Hedging Instruments                        
Derivative [Line Items]                        
Term of contract 15 years     3 years 14 years              
Initial notional amount of interest rate swaps | $ $ 10     $ 17   $ 10     $ 10     $ 27,900
Fixed interest rate (as percent) 3.19%     2.45% 3.74% 3.19%     3.19%      
Commodity swap contracts | Not Designated as Hedging Instrument                        
Derivative [Line Items]                        
Term of contract     1 year                  
Nonmonetary notional amount (in MMBtus) | MMBTU     323,390                  
Swap type, fixed price (in usd per MMBtu) | $ / MMBTU     2.84                  
Commodity swap contracts | Not Designated as Hedging Instrument | Commodity Swap Contract Effective May 2019                        
Derivative [Line Items]                        
Term of contract   1 year                    
Nonmonetary notional amount (in MMBtus) | MMBTU   437,004                    
Swap type, fixed price (in usd per MMBtu) | $ / MMBTU   2.68                    
Commodity swap contracts | Not Designated as Hedging Instrument | Commodity Swap Contract Effective May 2020                        
Derivative [Line Items]                        
Term of contract   1 year                    
Nonmonetary notional amount (in MMBtus) | MMBTU   435,810                    
Swap type, fixed price (in usd per MMBtu) | $ / MMBTU   2.70