Schedule I - Condensed Financial Information of the Parent (Condensed Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Cash and cash equivalents	$ 80,648	$ 52,499	$ 61,135	$ 95,390
Property, plant and equipment, net	131,049	132,539
Other non-current assets	26,557	24,618
Total assets	668,021	655,408	770,520
LIABILITIES AND EQUITY
Current liabilities	221,828	191,746
Other long-term liabilities	53,072	52,585
Stockholders’ equity	220,293	201,138
Total liabilities and equity	668,021	655,408
Parent Company
ASSETS
Cash and cash equivalents	57,917	22,506	$ 53,415	$ 94,035
Current intercompany accounts receivable, net	0	2,555
Other current assets	2,518	1,241
Investment in subsidiaries	185,559	205,024
Property, plant and equipment, net	935	1,276
Other non-current assets	13,870	8,534
Total assets	260,799	241,136
LIABILITIES AND EQUITY
Current liabilities	7,055	6,323
Current intercompany accounts payable, net	1,406	0
Other long-term liabilities	13,945	14,975
Stockholders’ equity	220,293	201,138
Total liabilities and equity	260,799	241,136
Parent Company | HBB
ASSETS
Investment in subsidiaries	44,057	51,377
Parent Company | KC
ASSETS
Investment in subsidiaries	21,394	31,750
Parent Company | NACoal
ASSETS
Investment in subsidiaries	105,645	108,381
Parent Company | Other
ASSETS
Investment in subsidiaries	14,463	13,516
Parent Company | Bellaire
LIABILITIES AND EQUITY
Note payable to Bellaire	$ 18,100	$ 18,700