Debt Senior Notes (Details) (USD $)	12 Months Ended							3 Months Ended		3 Months Ended		3 Months Ended			1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2012 Senior Notes [Member] 8.25% Interest Rate [Member]	Jun. 30, 2010 Senior Notes [Member] 8.25% Interest Rate [Member]	Mar. 31, 2012 Senior Notes [Member] 6.5% Interest Rate [Member]	Dec. 31, 2012 Senior Notes [Member] 6.5% Interest Rate [Member]	Mar. 31, 2012 Senior Notes [Member] 6.25% Interest Rate [Member]	Jun. 30, 2012 Senior Notes [Member] 6.25% Interest Rate [Member]	Mar. 31, 2012 Promissory Notes [Member]	Dec. 31, 2011 Promissory Notes [Member]	Mar. 31, 2012 Promissory Notes [Member] 6.25% Interest Rate [Member]	Apr. 30, 2012 Redemption of Senior Notes [Member] Senior Notes [Member] 6.25% Interest Rate [Member]
Debt Instrument [Line Items]
Principal							$ 150,000,000	$ 300,000,000
Proceeds from senior notes	294,750,000	0	[1]	147,540,000	[1]			294,800,000
Repayment of senior notes				(47,000,000)						157,800,000					27,200,000
Stated interest rate, senior notes						8.25%		6.50%	6.50%	6.25%	6.25%
Repayment of promissory notes		77,100,000		0								(72,900,000)	(77,100,000)	(72,900,000)
Credit agreement restrictions before 2015	206,000,000
Credit agreement restrictions 2015 to 2018	$ 171,000,000

[1] (1) Restated as described in Note 2.