Debt Promissory Notes (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Debt Instrument [Line Items]
Months, LIBOR Variable Rate	1 month
Repayments of Notes Payable	$ 77,100,000	$ 0	$ 0
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Notes Issued	150,000,000
Debt Instrument, Basis Spread on Variable Rate	3.50%
Debt Instrument, Increase (Decrease) Future Basis Spread on Variable Rate	0.25%
Repayments of Notes Payable	77,100,000
Notes Payable	$ 72,900,000