Derivatives (Cash Settlements) (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Derivative, Additional Cash Settlements Received (Paid) on Hedge	$ 282	$ (39)	$ 754	$ (415)
Natural Gas Contracts
Derivative [Line Items]
Derivative, Additional Cash Settlements Received (Paid) on Hedge	(65)	(36)	63	(234)
Interest Rate Swaps
Derivative [Line Items]
Derivative, Additional Cash Settlements Received (Paid) on Hedge	$ 347	$ (3)	$ 691	$ (181)