Fair Value Disclosure (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt excluding capital leases fair value	$ 153,400	$ 159,800	$ 177,600
Long-term debt excluding capital leases book value	153,400	159,800	177,600
Level 1 | Fair value measurements, recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mine Water Treatment Trust	7,347	$ 7,247	$ 7,279
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