Variable interest entities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Carrying amounts of consolidated assets and liabilities of variable interest entities
Current assets	$ 292,606	$ 360,453
Property, plant and equipment	1,147,743	1,107,657
Goodwill	162,497	161,460
Other assets	42,218	36,034
Total assets	1,913,930	1,930,869
Current liabilities	225,199	228,119
Other liabilities	14,590	14,139
Deferred income taxes	60,499	61,072
Total liabilities	968,471	978,344
Variable Interest Entity, Carrying Amount, Current Portion Of Long-term Debt, Consolidated VIE	1,795	1,784
Charleston Center LLC
Variable interest entities
Ownership percentage	19.90%
Carrying amounts of consolidated assets and liabilities of variable interest entities
Current assets	8,141	8,167
Property, plant and equipment	184,418	185,788
Goodwill	40,395	40,395
Other assets	1,963	2,185
Total assets	234,917	236,535
Current liabilities	6,520	6,101
Third-party debt, including $1,795 and $1,784 current portion	89,192	90,529
Other liabilities	14,590	14,139
Deferred income taxes	60,499	61,072
Total liabilities	170,801	171,841
Net assets (before amounts payable to OEH of $91,072 and $ 92,263)	64,116	64,694
Variable Interest Entity, Carrying Amount, Current Portion Of Long-term Debt, Consolidated VIE	1,795	1,784
Related Party Transaction, Due from (to) Related Party	$ (91,072)	$ (92,263)