Major Customers - Schedules of Percentages of Revenues and Receivables Associated with Significant Customers (Detail) - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sales Revenue, Net [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	51.00%	51.00%	34.00%
Receivables [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	50.00%	48.00%
Exxon Mobil Oil Corporation [Member] | Sales Revenue, Net [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	33.00%	27.00%	2.00%
Exxon Mobil Oil Corporation [Member] | Receivables [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	32.00%	30.00%
Chevron U.S.A. Inc. [Member] | Sales Revenue, Net [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	12.00%	16.00%	19.00%
Chevron U.S.A. Inc. [Member] | Receivables [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	11.00%	12.00%
Center Oil [Member] | Sales Revenue, Net [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	6.00%	8.00%	13.00%
Center Oil [Member] | Receivables [Member]
Entity Wide Revenue Major Customer [Line Items]
Total percentages of revenue and receivables associated with significant customers	7.00%	6.00%