Other Long-Term Assets and Other Income (Schedule of Other Long-Term Assets) (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Long-term assets:
Advance coal royalties		$ 9,296	$ 6,563
Marketable equity securities available for sale, at fair value (restricted)	[1]	2,036	1,763
Other		2,782	3,090
Other noncurrent assets total		$ 14,114	$ 11,416

[1] Held by Sunrise Indemnity, Inc., our wholly owned captive insurance company.