Derivative Financial Instruments (Details 2) (Designated as cash flow hedging instruments, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	$ 22	$ 4,482
Liability derivatives	7,419	5,683
Natural Gas Hedge
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives		4,050
Interest rate cap
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	22	432
Interest rate cap | Other current assets
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	12	143
Interest rate cap | Other long-term assets
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	10	289
Interest rate swaps
Entity's derivative instruments within the condensed consolidated balance sheets
Liability derivatives	7,419	5,683
Interest rate swaps | Other current liabilities
Entity's derivative instruments within the condensed consolidated balance sheets
Liability derivatives	4,000	1,800
Interest rate swaps | Other long-term liabilities
Entity's derivative instruments within the condensed consolidated balance sheets
Liability derivatives	$ 3,400	$ 3,900