Derivative Instruments (Details Textual) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended									6 Months Ended
	Aug. 31, 2011	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2007 Agreement	Jun. 30, 2013	Jun. 30, 2011	Jun. 30, 2012 6.50% notes due 2016 [Member]	Dec. 31, 2011 6.50% notes due 2016 [Member]	Jun. 30, 2011 6.50% notes due 2016 [Member]	Jun. 30, 2012 10.125% notes due 2015 [Member]	Dec. 31, 2011 10.125% notes due 2015 [Member]	Jun. 30, 2011 10.125% notes due 2015 [Member]	Jun. 30, 2011 Interest Rate Swap Agreement 1 [Member]	Jun. 30, 2011 Interest Rate Swap Agreement 2 [Member]
Derivative Instruments (Textual)
Variable rate basis				3-month LIBOR									6-month LIBOR	6-month LIBOR
Interest rate spread above London Interbank Offered Rate (LIBOR)				1.25%									4.05%	8.03%
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%
Coupon rate of notes							6.50%	6.50%	6.50%	10.125%	10.125%	10.125%
Notional amount for forward starting interest rate swap agreements				1,500,000,000
Long-term notes issued				325,000,000		1,100,000,000			500,000,000
Length of interest rate swap agreement (In years)				3 years
Number of forward starting interest rate swap agreements				15
Proceeds from (payments for) settlement of interest rate swap agreements				(89,777,000)
Estimated amount of pretax loss in AOCI related to interest rate swap that would be reclassified to earnings					6,055,000
Cash proceeds from interest rate swap agreements	25,382,000
Forward component of the settlement	23,387,000
Accrued interest income	1,995,000
Interest expense amortized		$ 1,004,000	$ 1,992,000