Debt - Revolver and Term Loans (Details) (USD $)	3 Months Ended	9 Months Ended															3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Jun. 30, 2013	Jun. 30, 2012 Revolver		Sep. 30, 2013 Five-Year Term Loan		Jun. 30, 2013 Five-Year Term Loan	Sep. 30, 2013 Seven Year Term Loan		Jun. 30, 2013 Seven Year Term Loan		Sep. 30, 2013 Unsecured Term Loan Due August 27, 2018		Jun. 30, 2013 Unsecured Term Loan Due August 27, 2018		Sep. 30, 2013 Revolving Credit Facility and Term Loans	Sep. 30, 2012 Revolving Credit Facility and Term Loans	Sep. 30, 2013 Interest Rate Contract Unsecured Term Loan Due August 27, 2018	Sep. 30, 2013 Interest Rate Contract Unsecured Term Loan Due August 27, 2018	Sep. 30, 2013 Interest Rate Contract Seven-Year Term Loan	Sep. 30, 2013 Interest Rate Contract Seven-Year Term Loan
Debt
Outstanding borrowings			$ 850,000,000	$ 0	[1]			$ 275,000,000			$ 225,000,000	[2]			$ 350,000,000	[3]
Interest rate (as a percent)						1.88%	[4]		4.04%	[2],[4]			3.25%	[3],[4]
Interest expense	3,584,000	8,532,000																	300,000	300,000	200,000	200,000
Unused commitment fee																	$ 300,000	$ 800,000

[1] Includes the unused facility fee of $0.3 million and $0.8 million for the three and nine months ended September 30, 2013, respectively.

[2] Includes interest expense related to an interest rate hedge of $0.2 million for both the three and nine months ended September 30, 2013.

[3] Includes interest expense related to an interest rate hedge of $0.3 million for both the three and nine months ended September 30, 2013.

[4] Interest rate at September 30, 2013 gives effect to interest rate hedges and LIBOR floors, as applicable.