Line of Credit Payable (Details) - USD ($)	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Revolving credit facility borrowing capacity	$ 900,000,000
Line of credit payable	63,200,000	$ 0
Line of Credit
Line of Credit Facility [Line Items]
Revolving credit facility borrowing capacity	900,000,000
Revolving credit facility weighted average outstanding balance	$ 2,918,000
Revolving credit facility weighted average interest rate	3.30%
Option to increase facility size	$ 1,600,000,000
Line of credit payable	63,200,000
Line of credit facility available for future borrowings	$ 836,800,000
Line of Credit | LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.875%