Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities - Summary of Active Derivative Instruments (Details)

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Derivative Instruments and Hedging Activities - Summary of Active Derivative Instruments (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
$ / MMBTU
Dec. 31, 2018
USD ($)
MMBTU
$ / MMBTU
Commodity Contract - April 2019 | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, term of contract 1 year  
Derivative, active commodity swap, fixed price (in usd per MMBtu) | $ / MMBTU 2.84 2.84
Initial notional amount, volume (in MMBtu) | MMBTU   323,390
Interest Rate Swap October 2029 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 9,200,000 $ 9,200,000
Derivative, active interest rate swap 5.77% 5.77%
Derivative, term of contract 11 years  
Interest Rate Swap June 2033 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 10,000,000 $ 10,000,000
Derivative, active interest rate swap 3.19% 3.19%
Derivative, term of contract 15 years  
Interest Rate Swap - December 2020 | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 17,100,000 $ 17,100,000
Derivative, active interest rate swap 2.46% 2.46%
Derivative, term of contract 3 years  
Interest Rate Swap - December 2027 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 14,100,000 $ 14,100,000
Derivative, active interest rate swap 4.74% 4.74%
Derivative, term of contract 10 years  
Interest Rate Swap - December 2038 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 14,084,000 $ 14,084,000
Derivative, active interest rate swap 3.26% 3.26%
Derivative, term of contract 15 years  
Interest Rate Swap - February 2023 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 20,746,000 $ 20,746,000
Derivative, active interest rate swap 2.19% 2.19%
Derivative, term of contract 7 years  
Interest Rate Swap - June 2028 - Contract 1 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 14,643,000 $ 14,643,000
Derivative, active interest rate swap 3.70% 3.70%
Derivative, term of contract 8 years  
Interest Rate Swap - June 2028 - Contract 2 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 10,734,000 $ 10,734,000
Derivative, active interest rate swap 3.70% 3.70%
Derivative, term of contract 8 years  
Interest Rate Swap - March 2020 - Contract 1 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 9,665,000 $ 9,665,000
Derivative, active interest rate swap 1.71% 1.71%
Derivative, term of contract 8 years  
Interest Rate Swap - March 2020 - Contract 2 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 7,085,000 $ 7,085,000
Derivative, active interest rate swap 1.71% 1.71%
Derivative, term of contract 8 years  
Interest Rate Swap - February 2021 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 3,256,000 $ 3,256,000
Derivative, active interest rate swap 5.30% 5.30%
Derivative, term of contract 15 years  
Interest Rate Swap - March 2024 | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Initial Notional Amount ($) $ 13,081,000 $ 13,081,000
Derivative, active interest rate swap 5.40% 5.40%
Derivative, term of contract 15 years 6 months  
Commodity Contract - April 2020 | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, active commodity swap, fixed price (in usd per MMBtu) | $ / MMBTU 2.68 2.68
Initial notional amount, volume (in MMBtu) | MMBTU   437,004
Commodity Contract - April 2021 | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, active commodity swap, fixed price (in usd per MMBtu) | $ / MMBTU 2.70 2.70
Initial notional amount, volume (in MMBtu) | MMBTU   435,810
Other liabilities | Hybrid Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair Value ($) $ 1,808,000 $ 1,808,000