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	Sep. 30, 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]									7,188,080	7,966,370			15,154,450
Price - Current Year | $ / bbl	[1]									51.87	51.69			51.77
Volume - Year One | bbl	[1]					5,455,007	5,765,318	6,131,170	6,581,629				23,933,124
Price - Year One | $ / bbl	[1]					51.54	51.68	51.84	52.01				51.78
Volume - Year Two | bbl	[1]	3,324,000	3,460,000	3,604,000	3,772,000							14,160,000
Price - Year Two | $ / bbl	[1]	53.61	53.59	53.58	53.6							53.59
Oil Basis Swaps [Member]
Derivative [Line Items]
Volume - Current Year | bbl	[2]									6,302,000	6,302,000			12,604,000
Price - Current Year | $ / bbl	[2]									(0.57)	(0.57)			(0.57)
Volume - Year One | bbl	[2]					5,488,000	5,765,000	6,156,000	6,586,000				23,995,000
Price - Year One | $ / bbl	[2]					(1.04)	(1.04)	(1.04)	(1.05)				(1.04)
Volume - Year Two | bbl	[2]	3,311,000	3,434,000	3,609,000	3,771,000							14,125,000
Price - Year Two | $ / bbl	[2]	(1.19)	(1.19)	(1.18)	(1.18)							(1.19)
Natural Gas Price Swaps [Member]
Derivative [Line Items]
Volume - Current Year | MMBTU	[3]									14,673,000	15,895,441			30,568,441
Price - Current Year | $ / MMBTU	[3]									3.1	3.12			3.11
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.