Line of Credit Payable (Details) - USD ($)	9 Months Ended
	Sep. 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	$ 85,997,000
Revolving credit facility weighted average interest rate	1.10%
Option to increase facility size	$ 1,000,000,000
Line of credit payable	282,400,000	$ 0
Line of credit facility available for future borrowings	$ 367,600,000
Line of Credit | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.925%