Derivative Instruments (Details Textual) (USD $)	12 Months Ended	37 Months Ended							6 Months Ended
	Dec. 31, 2007	Dec. 15, 2010	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2011 6.50% 5.5-year notes issued 2011 [Member]	Jun. 30, 2011 10.125% 7-year notes issued 2009 [Member]	Dec. 31, 2010 10.125% 7-year notes issued 2009 [Member]	Jun. 30, 2010 10.125% 7-year notes issued 2009 [Member]	Jun. 30, 2011 Interest Rate Swap Agreement 1 [Member]	Jun. 30, 2011 Interest Rate Swap Agreement 2 [Member]
Derivative Instruments (Textuals)
Coupon rate of notes					6.50%	10.125%	10.125%	10.125%
Derivative Instruments (Textuals)
Notional amount of interest rate swap agreement	$ 325,000,000								$ 500,000,000	$ 150,000,000
Fixed interest rate under swap agreement	5.25%								6.50%	10.125%
Maturity period of notes (in years)	3 years			7 years	5 years 6 months	7 years	7 years	7 years
Interest rate spread above London Interbank Offered Rate (LIBOR)		1.25%							4.05%	8.03%
Variable rate basis		3-month LIBOR							6-month LIBOR	6-month LIBOR
Aggregate notional amount of swaps	325,000,000			500,000,000
Length of interest rate swap agreement (In years)	3 years
Number of forward starting interest rate swap agreements	15
Notional amount for forward starting interest rate swap agreements	1,500,000,000
Cash payment for settlement of forward starting interest rate swap	89,777,000
Estimated amount of pretax loss accumulated in Other Comprehensive Income related to interest rate swap that would be reclassified to earnings			$ 6,247,000