Line of Credit and Notes Payable (Schedule of Long-Term Debt (excluding Bonds Payable)) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Loan payable	$ 949,070,000	$ 781,916,000
Less: Deferred financing costs related to term loans and notes payable, net of accumulated amortization	(1,930,000)	(2,084,000)
Credit Facilities | Revolving Credit Facility
Debt Instrument [Line Items]
Loan payable	501,000,000	334,000,000
Term Loans
Debt Instrument [Line Items]
Less: Deferred financing costs related to term loans and notes payable, net of accumulated amortization	(1,930,000)	(2,084,000)
Term Loans | $300 Million Term Loan
Debt Instrument [Line Items]
Loan payable	300,000,000	300,000,000
Face amount of issued debt instrument	300,000,000	300,000,000
Term Loans | $150 Million Term Loan
Debt Instrument [Line Items]
Loan payable	150,000,000	150,000,000
Face amount of issued debt instrument	$ 150,000,000	$ 150,000,000