Line of Credit Payable (Details) - USD ($)	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Revolving credit facility borrowing capacity	$ 650,000,000
Revolving credit facility weighted average outstanding balance	$ 33,241,000
Revolving credit facility weighted average interest rate	1.10%
Option to increase facility size	$ 1,000,000,000
Line of credit payable	127,500,000	$ 0
Line of credit facility available for future borrowings	$ 522,500,000
Line of Credit | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.925%