New Accounting Standards - Schedule of Impact of Adoption of New Lease Accounting Standard (Detail) - USD ($) $ in Thousands		Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets		$ 49,329
Accrued liabilities		399,822		$ 475,848
Operating lease liabilities – long-term		41,759
Asset retirement obligations and other liabilities		$ 319,079		$ 319,379
Accounting Standards Update 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets			$ 51,375
Accrued liabilities			(14,811)
Operating lease liabilities – long-term			(44,489)
Asset retirement obligations and other liabilities			7,925
Accounting Standards Update 2016-02 | Before Adoption
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets			59,300
Accrued liabilities			(14,811)
Operating lease liabilities – long-term			(44,489)
Accounting Standards Update 2016-02 | Reclassification
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets	[1]		(7,925)
Asset retirement obligations and other liabilities	[1]		$ 7,925

[1] As of December 31, 2018, we had $7.9 million primarily related to operating lease liabilities recorded as part of purchase price accounting related to building leases acquired because we did not expect to occupy the space or receive payments from our subleases. Lease incentives related to other buildings are also included. Upon adoption of the new standards update, these leases were included as part of our adoption but the ROU asset is reduced because we do not expect to use the asset.