Amendment of Revolving Credit Facility Amendment of Revolving Credit Facility (Details) (USD $)	3 Months Ended				0 Months Ended		0 Months Ended		0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Oct. 31, 2010 Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Apr. 24, 2013 Subsequent Event Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Apr. 23, 2013 Subsequent Event Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Apr. 24, 2013 Subsequent Event Maximum Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Apr. 23, 2013 Subsequent Event Maximum Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Apr. 24, 2013 Subsequent Event Minimum Revolving Credit Facility London Interbank Offered Rate (LIBOR)	Apr. 23, 2013 Subsequent Event Minimum Revolving Credit Facility London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount				$ 375,000,000		$ 500,000,000
Debt Instrument additional amount						225,000,000
Loan origination fees	$ (49,000)	$ 0			$ 2,000,000
Maturity Term					5 years
Debt Instrument, Description of Variable Rate Basis			LIBOR
Debt Instrument, Basis Spread on Variable Rate								3.00%		1.125%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage							0.45%		0.175%
Line of Credit Facility, Covenant Terms, Interest Coverage Ratio									3.0
Line of Credit Facility, Covenant Terms, Leverage Ratio							5.0		4.5
Line of Credit Facility, Covenant Terms,SeniorSecuredLeverage Ratio							3.5