Commitments (Narrative) (Details) - Natural Gas Per Thousand Cubic Feet [Member] - April 2018 to December 2020 [Member]	Mar. 31, 2018 MMcf / D $ / Mcf
Commitments and Contingencies Disclosure [Line Items]
Notional amount, per day \| MMcf / D	59
Swap price (per share) \| $ / Mcf	2.81

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant