Condensed Consolidating Financial Information (Details Textual) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Aug. 31, 2010	Mar. 19, 2013 5.125% Senior Notes Senior Notes	Dec. 31, 2013 6.625% Senior Notes Senior Notes	Mar. 19, 2013 6.625% Senior Notes Senior Notes	Feb. 10, 2011 6.625% Senior Notes Senior Notes	Oct. 03, 2013 5.875% Senior Notes Senior Notes
Debt Instrument [Line Items]
Stated interest rate		8.47%	5.125%	6.625%	6.625%	6.625%	5.875%
Aggregate principal amount of taxable revenue bonds			$ 300,000			$ 300,000	$ 250,000
Percentage of subsidiary owned	100.00%