Selected Quarterly Financial Data (Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Line Items]
Goodwill write-down				$ 411,786
Intangible assets, accumulated impairment			$ 38,351	38,351
Impairment charges					$ 8,445
Equity-based compensation expense				20,318	18,446	$ 15,397
Equity-based compensation expense, net of taxes				12,587	$ 11,372	$ 9,508
Exploration and Production [Member]
Quarterly Financial Data [Line Items]
Goodwill write-down	$ 411,786			411,786
Indefinite-lived intangible asset write-down	38,300		$ 38,351
Impairment charges		$ 8,445		$ 67,647
Impairments on long-lived assets	63,928
Decrease in contingent consideration	$ 20,642