Notes Payable (Details) (USD $)			1 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Aug. 31, 2012 Two Thousand Twenty Two Notes [Member]
Debt Instrument [Line Items]
Principal amount of debt			$ 325,000,000
Stated interest rate			3.80%
Proceeds from Issuance of Long-term Debt			320,011,000
Notes payable, unamortized discount	9,571,000	5,033,000	4,989,000
Debt Instrument, Interest Rate, Effective Percentage			3.98%
Proceeds From Issuance of Long-term Debt, Net of Debt Issuance Costs			317,094,000
Debt Issuance Cost			$ 2,917,000