Income Taxes Additional Information (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Income Tax Disclosure [Abstract]
Income Tax Examination, Increase (Decrease) in Liability from Prior Year		$ 1,585
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	5,144
Income Tax Reconciliation, Nondeductible Expense, Depletion	20,480	25,471
Uncertain tax positions	2,540	22,770
Uncertain tax positions that, if recognized, would impact effective tax rate	1,651	2,071
Accrued interest liability relating to uncertain tax positions	1,302	6,200
Interest expense included in accrued interest liability	$ (4,898)	$ 675