Notes and Bonds Payable - Details of Mortgage Notes (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) mortgage_note_payable mortgage_loan	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Number of outstanding mortgage notes \| mortgage_loan	17
Mortgage Notes [Member]
Debt Instrument [Line Items]
Investment in Collateral	$ 400.2
Mortgage notes payable carrying amount	$ 143.2	$ 155.4
Number of outstanding mortgage notes \| mortgage_loan	18
Mortgage Notes [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Contractual interest rates	6.90%
Mortgage Notes [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Contractual interest rates	3.30%
Mortgage Notes [Member] \| Mortgage Notes 5.54% [Member] \| Insurance Company [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7.3
Effective Interest rate	5.54%
Maturity Date	2018-12
Collateral	MOB
Principal and Interest Payments	Monthly/25-yr amort.
Principal and interest amortization period	25 years
Investment in Collateral	$ 0.0
Mortgage notes payable carrying amount	0.0	6.0
Unemcumbered gross investment	14.4
Mortgage Notes [Member] \| Mortgage Notes 5.07% [Member] \| Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.5
Effective Interest rate	5.07%
Maturity Date	2019-03
Collateral	MOB
Principal and Interest Payments	Monthly/5-yr amort.
Principal and interest amortization period	5 years
Investment in Collateral	$ 0.0
Mortgage notes payable carrying amount	0.0	9.3
Unemcumbered gross investment	14.1
Mortgage Notes [Member] \| Mortgage Notes 4.55% [Member] \| Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.4
Effective Interest rate	4.55%
Maturity Date	2019-07
Collateral	MOB
Principal and Interest Payments	Monthly/8-yr amort
Principal and interest amortization period	8 years
Investment in Collateral	$ 27.8
Mortgage notes payable carrying amount	9.0	9.2
Unamortized premium	0.3
Mortgage Notes [Member] \| Mortgage Notes 7.65% [Member] \| Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 15.2
Effective Interest rate	7.65%
Maturity Date	2020-07
Collateral	MOB
Principal and interest amortization period	11 years
Investment in Collateral	$ 20.2
Mortgage notes payable carrying amount	12.5	12.7
Unaccreted discount	$ 2.4
Period for monthly installments of interest	24 months
Mortgage Notes [Member] \| Mortgage Notes 4.00% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7.9
Effective Interest rate	4.00%
Maturity Date	2020-08
Collateral	MOB
Principal and Interest Payments	Monthly/15-yr amort.
Principal and interest amortization period	15 years
Investment in Collateral	$ 20.7
Mortgage notes payable carrying amount	1.3	2.0
Unamortized premium	0.3
Mortgage Notes [Member] \| Mortgage Notes 5.25% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7.3
Effective Interest rate	5.25%
Maturity Date	2020-08
Collateral	MOB
Principal and Interest Payments	Monthly/27-yr amort.
Principal and interest amortization period	27 years
Investment in Collateral	$ 18.0
Mortgage notes payable carrying amount	6.2	6.5
Unamortized premium	0.4
Mortgage Notes [Member] \| Mortgage Notes 4.30% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 5.6
Effective Interest rate	4.30%
Maturity Date	2021-01
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 15.7
Mortgage notes payable carrying amount	4.6	4.8
Unamortized premium	0.2
Mortgage Notes [Member] \| Mortgage Notes 6.43% [Member] \| Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12.9
Effective Interest rate	6.43%
Maturity Date	2021-02
Collateral	MOB
Principal and Interest Payments	Monthly/12-yr amort.
Principal and interest amortization period	12 years
Investment in Collateral	$ 55.1
Mortgage notes payable carrying amount	10.3	10.5
Unaccreted discount	1.0
Mortgage Notes [Member] \| Mortgage Notes 3.87% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11.0
Effective Interest rate	3.87%
Maturity Date	2022-11
Collateral	MOB
Principal and Interest Payments	Monthly/7-yr amort.
Principal and interest amortization period	7 years
Investment in Collateral	$ 22.0
Mortgage notes payable carrying amount	10.2	10.4
Unaccreted discount	0.1
Mortgage Notes [Member] \| Mortgage Notes 3.86% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12.3
Effective Interest rate	3.86%
Maturity Date	2023-08
Collateral	MOB
Principal and Interest Payments	Monthly/7-yr amort.
Principal and interest amortization period	7 years
Investment in Collateral	$ 25.4
Mortgage notes payable carrying amount	11.2	11.5
Unaccreted discount	0.2
Mortgage Notes [Member] \| Mortgage Notes 4.27% [Member] \| Financial Services [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12.4
Effective Interest rate	4.27%
Maturity Date	2023-10
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 24.9
Mortgage notes payable carrying amount	12.0	12.2
Unamortized premium	0.4
Mortgage Notes [Member] \| Mortgage Notes 4.84% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.0
Effective Interest rate	4.84%
Maturity Date	2023-12
Collateral	MOB,OFC
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 25.3
Mortgage notes payable carrying amount	7.8	0.0
Unamortized premium	0.1
Mortgage Notes [Member] \| Mortgage Notes 4.13% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 13.3
Effective Interest rate	4.13%
Maturity Date	2024-01
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 21.2
Mortgage notes payable carrying amount	13.0	13.3
Unamortized premium	0.8
Mortgage Notes [Member] \| Mortgage Notes 3.96% [Member] \| Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 6.8
Effective Interest rate	3.96%
Maturity Date	2024-02
Collateral	MOB
Principal and Interest Payments	Monthly/7-yr amort.
Principal and interest amortization period	7 years
Investment in Collateral	$ 14.5
Mortgage notes payable carrying amount	6.6	6.7
Unamortized premium	0.2
Mortgage Notes [Member] \| Mortgage Notes 4.32% [Member] \| Financial Services [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9.7
Effective Interest rate	4.32%
Maturity Date	2024-09
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 16.5
Mortgage notes payable carrying amount	8.6	8.8
Unamortized premium	0.1
Mortgage Notes [Member] \| Mortgage Notes 3.71% [Member] \| Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11.5
Effective Interest rate	3.71%
Maturity Date	2026-01
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 38.4
Mortgage notes payable carrying amount	10.1	10.5
Mortgage Notes [Member] \| Mortgage Notes 5.25% 20 Year [Member] \| Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 15.0
Effective Interest rate	5.25%
Maturity Date	2027-04
Collateral	MOB
Principal and Interest Payments	Monthly/20-yr amort.
Principal and interest amortization period	20 years
Investment in Collateral	$ 33.5
Mortgage notes payable carrying amount	8.8	9.6
Unamortized premium	0.7
Mortgage Notes [Member] \| Mortgage Notes 4.79% [Member] \| Municipal Government [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11.0
Effective Interest rate	4.79%
Collateral	MOB
Principal and Interest Payments	Semi-Annual
Investment in Collateral	$ 21.0
Mortgage notes payable carrying amount	11.0	$ 11.4
Unamortized premium	$ 1.0
Number of outstanding mortgage notes \| mortgage_note_payable	3

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