Fair Value (Quantitative Information) (Details) - Natural Gas Exchange Agreements [Member] $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) MMBTU $ / MmBtu	Dec. 31, 2018 USD ($)
Fair Value, Measurements, Recurring [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Derivative Liability | $	$ (2,992)	$ (2,774)
Sales [Member] | Minimum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Derivative, Forward Price | $ / MmBtu	1.45
Transaction/Delivery Volumes | MMBTU	60,000
Sales [Member] | Maximum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Derivative, Forward Price | $ / MmBtu	3.62
Transaction/Delivery Volumes | MMBTU	310,000
Purchase [Member] | Minimum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Derivative, Forward Price | $ / MmBtu	1.37
Transaction/Delivery Volumes | MMBTU	118,162
Purchase [Member] | Maximum [Member] | Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Derivative, Forward Price | $ / MmBtu	2.30
Transaction/Delivery Volumes | MMBTU	310,000