Derivative Instruments - Notional Amounts of Derivative Instruments (Details) $ in Thousands, Mcf in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) Mcf	Dec. 31, 2019 USD ($) Mcf
Commodity Member
Derivative [Line Items]
Notional amount	1,280.9	1,460.6
Basis Swap
Derivative [Line Items]
Notional amount	1,311.8	1,290.4
Interest Rate Swap
Derivative [Line Items]
Derivative notional amount | $	$ 575,625	$ 160,000
Commodity Swap Purchased
Derivative [Line Items]
Notional amount	5.7
Basis Swap Purchased
Derivative [Line Items]
Notional amount	3.8