Related Parties (Narrative) (Details)	12 Months Ended
Dec. 31, 2018 USD ($) $ / Square_Foot Rate shares	Dec. 31, 2017 USD ($) $ / Square_Foot	Dec. 31, 2016 USD ($) $ / Square_Foot
Tower Property [Member]
Percentage of Tower stock owned by the Company's Executive Officers \| Rate	67.00%
Company stock owned by Tower \| shares	201,901
Tower's long-term line of credit with the Bank	$ 13,500,000
Debt Instrument, Unused Borrowing Capacity, Fee	9,100,000
Tower's maximum amount outstanding on the line of credit during period	0	$ 5,200,000	$ 0
Tower's line of credit, current balance	0	0	0
Tower's letters of credit outstanding, amount	0	0	0
Tower's line of credit facility, commitment fee amount	0	0	0
Tower's long-term construction loan	0	0	0
Rent paid to the Company by Tower	$ 74,000	$ 74,000	$ 72,000
Rent per square foot \| $ / Square_Foot	16.69	15.75	15.67
Executive Chairman [Member]
State tax credits sold by the Company to related party	$ 831,000	$ 694,000	$ 549,000
Former Vice Chairman [Member]
State tax credits sold by the Company to related party	759,000	598,000	244,000
Chief Executive Officer [Member]
State tax credits sold by the Company to related party	119,000	67,000	72,000
Former Chief Executive Officer [Member]
State tax credits sold by the Company to related party	$ 0	$ 0	$ 191,000

Line of Credit, Available Borrowing Capacity (considers amount of collateral pledged).

No definition available.

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- Definition

Percentage of outstanding Tower Properties Company stock owned by the Company's Chief Executive Officer and Vice Chairman, together with members of their immediate families.

+ References

No definition available.

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- Definition

Number of Company shares owned by Tower Properties Company (a related party).

+ References

No definition available.

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- Definition

Rent revenue that we (the Company) received from our lessee.

+ References

No definition available.

+ Details

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Data Type:	us-types:perUnitItemType
Balance Type:	na
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- Definition

Sales of state tax credits arising from third party property redevelopment. These were primarily purchased by the Company with the purpose of reselling to third parties.

+ References

No definition available.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of the fee for available but unused credit capacity under the credit facility.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Maximum amount borrowed under the credit facility at any time during the period.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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- Definition

This element represents the current and noncurrent portions of a long-term real estate loan with an initial maturity beyond one year or beyond the normal operating cycle, if longer, to finance building costs. The funds are disbursed as needed or in accordance with a prearranged plan; generally, a portion of the funds is disbursed at inception and the remainder as construction progresses. The money is repaid on completion of the project (generally one to seven years), usually from the proceeds of a mortgage loan. The rate is normally higher than the prime rate, and there is usually an origination fee. The effective yield on these loans tends to be high, and the lender has a security interest in the real property.

+ References

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- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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