Notes Payable (Term Loan) (Details) - Term Loan	6 Months Ended
	Jun. 30, 2019 USD ($)
Debt Instrument [Line Items]
Unsecured term loan	$ 250,000,000
LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.20%
LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.20%
LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.70%
Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.50%
One-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.00%
Base Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.00%
Base Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.75%