Fair Value (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Level 1
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	$ 0	$ 0
Level 2
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	(14,384)	(4,023)
Level 3
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	0	0
Commodity futures natural gas contracts | Level 1
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	0	0
Commodity futures natural gas contracts | Level 2
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	(941)	265
Commodity futures natural gas contracts | Level 3
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	0	0
Interest Rate Swaps | Level 1
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	0	0
Interest Rate Swaps | Level 2
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	(13,443)	(4,288)
Interest Rate Swaps | Level 3
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	0	0
Total
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	(14,384)	(4,023)
Total | Commodity futures natural gas contracts
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	(941)	265
Total | Interest Rate Swaps
Fair Value of Financial Instruments
Fair Value, Net Asset (Liability)	$ (13,443)	$ (4,288)