Notes Payable, Revolving Credit Facility, Interest and Amortization of Deferred Debt Costs - Scheduled Maturities of Debt, Including Scheduled Principal Amortization (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Balloon Payments
July 1 through December 31, 2019	$ 0
2020	61,163
2021	11,012
2022	84,502
2023	84,225
2024	66,640
Thereafter	474,181
Principal amount	781,723
Scheduled Principal Amortization
July 1 through December 31, 2019	14,675
2020	28,537
2021	28,334
2022	28,925
2023	29,315
2024	27,894
Thereafter	115,902
Principal amount	273,582
Total
July 1 through December 31, 2019	14,675
2020	89,700
2021	39,346
2022	113,427
2023	113,540
2024	94,534
Thereafter	590,083
Principal amount	1,055,305	$ 1,000,000
Unamortized deferred debt costs	10,001	10,300
Net	1,045,304
Debt Instrument [Line Items]
Outstanding line of credit	46,600	45,329
Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Outstanding line of credit	$ 48,000	$ 47,000

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount of payment greater than the preceding installment payments to be paid at final maturity date of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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