Interest Expense (Tables)

6 Months Ended

Jun. 30, 2015

Interest Costs Incurred [Abstract]

Interest income and expense

			Three Months Ended				Six Months Ended
			June 30,				June 30,
			2015		2014		2015		2014
Senior notes			$	9,563	$	9,563	$	19,125	$	21,577
Credit facility unutilized fee				649		562		1,384		1,223
Federal coal lease obligations imputed interest				1,488		2,612		2,847		5,224
Amortization of deferred financing costs and
	original issue discount			1,030		1,027		2,094		2,163
Other				45		68		93		145
		Subtotal		12,775		13,832		25,543		30,332
Premium on early retirement of debt				—		—		—		13,837
Write-off of deferred financing costs
	and original issue discount			—		—		—		7,338
Other				—		16		—		364
		Total cost of early retirement of debt and refinancings		—		16		—		21,538
Total interest expense				12,775		13,848		25,543		51,870
Less interest capitalized				(154)		(35)		(254)		(63)
Net interest expense			$	12,621	$	13,813	$	25,289	$	51,807