Accrued Liabilities and Deferred Credits (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts Payable and Accrued Liabilities [Line Items]
Accrued compensation	$ 3,529	$ 1,687
Environmental and insurance liabilities	1,621	1,887
Deferred revenue	27,158	29,859
Legal	357	2,972
Other accrued liabilities	9,687	11,086
Total accrued liabilities and deferred credits	$ 42,352	$ 47,491