Notes and Bonds Payable - Details of Mortgage Notes (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) mortgage_note_payable	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Number of outstanding mortgage notes | mortgage_note_payable	14
Mortgage notes payable [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 114,934	$ 128,161
Investment in Collateral	285,000
Mortgage notes payable carrying amount	115,600	128,700
Unaccreted discount	1,450	1,779
Unamortized premium	$ 2,569	2,704
Number of outstanding mortgage notes | mortgage_note_payable	17
Mortgage notes payable [Member] | Mortgage Notes 5% 25 Year [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 13,100
Effective Interest rate	5.00%
Maturity Date	2016-04
Collateral	MOB
Principal and Interest Payments	Monthly/25-yr amort.
Principal and interest amortization period	25 years
Investment in Collateral	$ 0
Mortgage notes payable carrying amount	0	10,200
Unamortized premium	600
Mortgage notes payable [Member] | Mortgage Notes 4.540% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 8,100
Effective Interest rate	4.54%
Maturity Date	2016-08
Collateral	MOB
Principal and Interest Payments	Monthly/10-yr amort.
Principal and interest amortization period	10 years
Investment in Collateral	$ 0
Mortgage notes payable carrying amount	0	7,400
Unamortized premium	200
Mortgage notes payable [Member] | Mortgage Notes 5% 30 Year [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 18,300
Effective Interest rate	5.40%
Maturity Date	2016-12
Collateral	MOB
Principal and Interest Payments	Monthly/30-yr amort.
Principal and interest amortization period	30 years
Investment in Collateral	$ 0
Mortgage notes payable carrying amount	0	16,000
Unamortized premium	300
Mortgage notes payable [Member] | Mortgage Notes 7.770% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 4,700
Effective Interest rate	7.77%
Maturity Date	2017-01
Collateral	MOB
Principal and Interest Payments	Monthly/20-yr amort.
Principal and interest amortization period	20 years
Investment in Collateral	$ 0
Mortgage notes payable carrying amount	0	400
Mortgage notes payable [Member] | Mortgage Notes 5.530% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7,000
Effective Interest rate	5.53%
Maturity Date	2018-01
Collateral	MOB
Principal and Interest Payments	Monthly/15-yr amort.
Principal and interest amortization period	15 years
Investment in Collateral	$ 14,300
Mortgage notes payable carrying amount	700	1,400
Mortgage notes payable [Member] | Mortgage Notes 5.54% [Member] | Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7,300
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	$ 14,200
Mortgage notes payable carrying amount	6,200	6,500
Unamortized premium	2,400
Mortgage notes payable [Member] | Mortgage Notes 5.070% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9,500
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	$ 13,900
Mortgage notes payable carrying amount	9,500	9,700
Unamortized premium	300
Mortgage notes payable [Member] | Mortgage Notes 4.55% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9,400
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	$ 27,800
Mortgage notes payable carrying amount	9,300	9,500
Unamortized premium	400
Mortgage notes payable [Member] | Mortgage Notes 7.650% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 15,200
Effective Interest rate	7.65%
Maturity Date	2020-07
Collateral	MOB
Principal and Interest Payments	-18
Principal and interest amortization period	11 years
Investment in Collateral	$ 20,200
Mortgage notes payable carrying amount	12,700	12,700
Unaccreted discount	$ 1,000
Period for monthly installments of interest	24 months
Mortgage notes payable [Member] | Mortgage Notes 4.000% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7,900
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	$ 20,700
Mortgage notes payable carrying amount	2,700	3,300
Unamortized premium	800
Mortgage notes payable [Member] | Mortgage Notes 5.25% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 7,300
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	$ 17,900
Mortgage notes payable carrying amount	6,700	6,900
Unamortized premium	100
Mortgage notes payable [Member] | Mortgage Notes 6.430% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 12,900
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	$ 19,900
Mortgage notes payable carrying amount	10,700	10,800
Unaccreted discount	700
Mortgage notes payable [Member] | Mortgage Notes 4.13% [Member] | Life Insurance Co. [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 13,300
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	$ 20,500
Mortgage notes payable carrying amount	13,600	0
Mortgage notes payable [Member] | Mortgage Notes 4.320% [Member] | Financial Services [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 9,700
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	$ 16,100
Mortgage notes payable carrying amount	9,100	9,300
Mortgage notes payable [Member] | Mortgage Notes 3.710% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11,500
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	$ 37,300
Mortgage notes payable carrying amount	11,000	0
Mortgage notes payable [Member] | Mortgage Notes 5.25% 20 Year [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 15,000
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	$ 33,400
Mortgage notes payable carrying amount	10,400	11,100
Mortgage notes payable [Member] | Mortgage Notes 5.550% [Member] | Commercial Bank [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 1,800
Effective Interest rate	5.55%
Maturity Date	2030-10
Collateral	OTH
Principal and Interest Payments	Monthly/27-yr amort.
Principal and interest amortization period	27 years
Investment in Collateral	$ 7,900
Mortgage notes payable carrying amount	1,300	1,400
Mortgage notes payable [Member] | Mortgage Notes 4.790% [Member] | Municipal Government [Member]
Debt Instrument [Line Items]
Mortgage notes	$ 11,900
Effective Interest rate	4.79%
Collateral	MOB
Principal and Interest Payments	Semi-Annual (17)
Investment in Collateral	$ 20,900
Mortgage notes payable carrying amount	11,700	$ 12,100
Unamortized premium	$ 1,000
Number of outstanding mortgage notes | mortgage_note_payable	4
Maximum [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Contractual interest rates	6.88%
Minimum [Member] | Mortgage notes payable [Member]
Debt Instrument [Line Items]
Contractual interest rates	3.60%