Derivative Financial Instruments (Outstanding Commodity Derivative Contracts) (Detail) - Minimum [Member]		3 Months Ended									12 Months Ended
		Dec. 31, 2019 MMBTU bbl $ / bbl $ / MMBTU	Sep. 30, 2019 MMBTU bbl $ / bbl $ / MMBTU	Jun. 30, 2019 MMBTU bbl $ / bbl $ / MMBTU	Mar. 31, 2019 MMBTU bbl $ / bbl $ / MMBTU	Dec. 31, 2018 MMBTU bbl $ / bbl $ / MMBTU	Sep. 30, 2018 MMBTU bbl $ / bbl $ / MMBTU	Jun. 30, 2018 MMBTU bbl $ / bbl $ / MMBTU	Mar. 31, 2018 MMBTU bbl $ / bbl $ / MMBTU	Dec. 31, 2017 MMBTU bbl $ / bbl $ / MMBTU	Dec. 31, 2019 MMBTU bbl $ / bbl $ / MMBTU	Dec. 31, 2018 MMBTU bbl $ / bbl $ / MMBTU	Dec. 31, 2017 MMBTU bbl $ / bbl $ / MMBTU
Oil Price Swaps [Member]
Derivative [Line Items]
Volume - Current Year | bbl	[1]									9,370,080			9,370,080
Price - Current Year | $ / bbl	[1]									51.33			51.33
Volume - Year One | bbl	[1]					6,676,007	7,064,318	7,546,170	8,180,629			29,467,124
Price - Year One | $ / bbl	[1]					51.26	51.36	51.45	51.54			51.41
Volume - Year Two | bbl	[1]	4,721,000	4,897,000	5,090,000	5,314,000						20,022,000
Price - Year Two | $ / bbl	[1]	52.55	52.54	52.52	52.54						52.54
Oil Basis Swaps [Member]
Derivative [Line Items]
Volume - Current Year | bbl	[2]									8,508,000			8,508,000
Price - Current Year | $ / bbl	[2]									(0.74)			(0.74)
Volume - Year One | bbl	[2]					6,684,000	6,961,000	7,521,000	7,936,000			29,102,000
Price - Year One | $ / bbl	[2]					(1.01)	(1.01)	(1.01)	(1.02)			(1.01)
Volume - Year Two | bbl	[2]	4,139,000	4,262,000	4,428,000	4,581,000						17,410,000
Price - Year Two | $ / bbl	[2]	(1.18)	(1.18)	(1.17)	(1.17)						(1.17)
Natural Gas Price Swaps [Member]
Derivative [Line Items]
Volume - Current Year | MMBTU	[3]									14,673,000			14,673,000
Price - Current Year | $ / MMBTU	[3]									3.1			3.1
Volume - Year One | MMBTU	[3]					9,904,000	10,219,000	10,641,000	11,156,000			41,920,000
Price - Year One | $ / MMBTU	[3]					3.04	3.05	3.05	3.06			3.05
Volume - Year Two | MMBTU	[3]	2,489,535	2,578,537	2,681,387	2,791,533						10,540,992
Price - Year Two | $ / MMBTU	[3]	2.85	2.85	2.85	2.86						2.85

[1] The index prices for the oil price swaps are based on the New York Mercantile Exchange (“NYMEX”) – West Texas Intermediate (“WTI”) monthly average futures price.

[2] The basis differential price is between Midland – WTI and Cushing – WTI.

[3] The index prices for the natural gas price swaps are based on the NYMEX – Henry Hub last trading day futures price.