Accrued Liabilities and Deferred Credits (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Payables and Accruals [Abstract]
Employee-related Liabilities, Current	$ 3,705	$ 3,529
Deferred revenue	29,996	27,962
Environmental and insurance liabilities	1,071	1,621
Other accrued liabilities	14,875	9,240
Total accrued liabilities and deferred credits	$ 49,647	$ 42,352