Derivative Financial Instruments (Details 2) (Designated as cash flow hedging instruments, USD $)	Jun. 30, 2012	Dec. 31, 2011
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	$ 81,000	$ 4,482,000
Natural Gas Hedge
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives		4,050,000
Interest rate cap
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	81,000	432,000
Interest rate cap | Other current assets
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	39,000	143,000
Interest rate cap | Other long-term assets
Entity's derivative instruments within the condensed consolidated balance sheets
Asset derivatives	42,000	289,000
Interest rate swaps
Entity's derivative instruments within the condensed consolidated balance sheets
Liability derivatives	6,594,000	5,683,000
Interest rate swaps | Other current liabilities
Entity's derivative instruments within the condensed consolidated balance sheets
Liability derivatives	3,100,000	1,800,000
Interest rate swaps | Other long-term liabilities
Entity's derivative instruments within the condensed consolidated balance sheets
Liability derivatives	$ 3,500,000	$ 3,900,000