Organization and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended					12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Organization And Summary Of Significant Accounting Policies [Line Items]
Tax benefit from US tax reform legislation						$ 0	$ (713,655)	$ 0
Accrued litigation settlement	$ 19,753				$ 59,600	19,753	59,600
Cumulative Effect on Retained Earnings, Net of Tax							5,150
Allowance for Doubtful Accounts Receivable	2,400				2,200	2,400	2,200
Unamortized Debt Issuance Expense	45,100				55,000	45,100	55,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount						300	400	1,000
Cash deposits in excess of federally insured amounts	280,700					280,700
Net asset retirement costs	57,700				40,000	57,700	40,000
Capitalized debt issue costs, relating to long-term debt	51,200				58,200	51,200	58,200
Accumulated amortization, relating to capitalized debt issue costs	62,500				51,800	62,500	51,800
Amortization expense related to capitalized debt issuance costs						9,300	9,100	9,800
Deferred Tax Assets, Valuation Allowance	19,633				$ 19,341	19,633	19,341
Transportation expenses	49,000	$ 46,000	$ 47,300	$ 49,300		191,587	0	$ 0
Estimated litigation liability, after tax							$ 37,000
Basic eps litigation settlement					$ 0.10
Diluted eps estimated litigation settlement							$ 0.10
Revolving Credit Facility [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Unamortized Debt Issuance Expense	$ 6,100				$ 3,200	$ 6,100	$ 3,200
Customer one concentration [Member] | Oil And Natural Gas [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage of crude oil sales to one single purchaser accounted on total revenues						12.00%