Fair Value Disclosure (Narrative) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt excluding capital leases fair value	$ 177,600,000	$ 236,300,000	$ 210,600,000
Long-term debt excluding capital leases book value	177,600,000	236,300,000	210,600,000
Level 1 | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mine Water Treatment Trust	7,279,000	7,220,000	6,638,000
Bellaire Corporation | Level 1 | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mine Water Treatment Trust	$ 5,000,000