Related Party Transactions - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended			1 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2012 Bbls	Aug. 31, 2012
Related Party Transaction [Line Items]
Deferred Income Taxes Associated With Acquired Properties			$ 57,000,000
Asset Retirement Obligations Assumed In Acquisition			600,000
Revenues from transactions with related party		95,128,000	100,405,000	58,892,000
Due from affiliates		13,100,000	12,700,000
Due to Affiliate		300,000	200,000
Expenses from transactions with related party		700,000
Related party transaction, due to related party		1,200,000
Production expenses to affiliates		5,123,000	1,408,000	1,974,000
Total amount paid to related party		58,200,000	48,500,000	32,700,000
Due to affiliates		5,600,000	5,100,000
Amount charged to affiliate for aircraft use		51,000	55,000	112,000
Amount charged to company by affiliate for aircraft use		97,000	51,000	102,000
Issuance of common stock to acquire property, in shares	7.8			7.8
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Consideration cost	279,000,000
Purchase price adjustment arising after closing date			500,000
Oil And Natural Gas [Member]
Related Party Transaction [Line Items]
Joint Interest Obligations Assumed In Acquisition			38,000,000
Net book value			177,000,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party				1,900,000
Number of barrels sold to affiliate				21,000
Number of barrels purchased from affiliate			30,000	2,000
Purchases from transactions with related party			3,000,000	200,000
Expenses from transactions with related party		1,800,000
Capitalized costs	5,000,000	5,900,000	5,700,000	5,000,000
Production expenses to affiliates		5,100,000	1,400,000	2,000,000
Total amount paid to related party		1,900,000
Related Party Transaction Transportation Contract Period		5
Crude Oil Pipeline Capacity Per Day					10,000
Related Party Transaction Transportation Charges For Crude Oil Per Barrel					5.25
Contractual Obligation		96,000,000
Officers And Other Key Employees [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party		800,000	1,300,000	38,500,000
Total amount paid to related party		0		300,000
Due to affiliates		100,000	200,000
Revenues paid to related party		1,700,000	2,300,000	38,300,000
Due from affiliates		200,000	400,000
Other Affiliates [Member]
Related Party Transaction [Line Items]
Total amount paid to related party		34,000	238,000
Total amount received from related party		39,000	379,000
Wheatland Oil Inc. [Member] | Chief Executive Officer [Member]
Related Party Transaction [Line Items]
CEO ownership in related party						75.00%
Wheatland Oil Inc. [Member] | Vice Chairman [Member]
Related Party Transaction [Line Items]
Vice Chairman ownership in related party						25.00%
Wheatland [Member]
Related Party Transaction [Line Items]
Net book value			82,000,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Revenues from transactions with related party			$ 100,400,000	$ 57,000,000