Business Segments (Data by Geographic Region) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 286,519	$ 239,107	$ 196,500	$ 193,734	$ 297,285	$ 221,714	$ 200,370	$ 177,413	$ 915,860	$ 896,782	$ 932,666
Long-lived assets	157,182				187,896				157,182	187,896	252,388
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									795,071	779,890	813,609
Long-lived assets	151,618				182,116				151,618	182,116	246,902
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									120,789	116,892	119,057
Long-lived assets	5,564				5,780				5,564	5,780	5,486
HBB
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	204,895	163,291	129,498	123,293	204,818	135,155	118,385	101,325	620,977	559,683	547,790
NACoal
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 26,033	$ 42,704	$ 37,942	$ 41,319	$ 33,210	$ 49,840	$ 49,780	$ 39,872	$ 147,998	$ 172,702	$ 193,651