Line of Credit Payable (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Revolving credit facility borrowing capacity	$ 500,000,000
Revolving credit facility weighted average outstanding balance	55,144,000
Revolving credit facility weighted average interest rate	1.20%
Maturity date	Oct. 01, 2016
Option to extend maturity date	Oct. 01, 2017
Option to increase facility size	1,000,000,000
Line of credit payable	0	46,400,000
Line of credit facility available for future borrowings	$ 500,000,000
Line of Credit
Line of Credit Facility [Line Items]
Debt instrument, description of variable rate basis	LIBOR plus 107.5 basis points
Basis spread on variable rate	1.075%