Organization, Consolidation and Presentation of Financial Statements	6 Months Ended
Jun. 30, 2011
Organization, Consolidation and Presentation of Financial Statements
Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block]	Note A – Basis of Presentation The accompanying unaudited financial statements of National Property Investors 4 (the "Partnership" or the "Registrant") have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 8-03 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of NPI Equity Investments, Inc. (“NPI Equity” or the "Managing General Partner"), all adjustments (consisting of normal recurring items) considered necessary for a fair presentation have been included. Operating results for the three and six month periods ended June 30, 2011 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2011. The balance sheet at December 31, 2010 has been derived from the audited financial statements at that date but does not include all of the information and disclosures required by generally accepted accounting principles for complete financial statements. For further information, refer to the financial statements and footnotes thereto included in the Partnership's Annual Report on Form 10-K for the fiscal year ended December 31, 2010. The Managing General Partner is a subsidiary of Apartment Investment and Management Company ("Aimco"), a publicly traded real estate investment trust. The Partnership’s management evaluated subsequent events through the time this Quarterly Report on Form 10-Q was filed. Certain reclassifications have been made to the 2010 balances to conform to the 2011 presentation. On July 28, 2011, the Partnership entered into an agreement and plan of conversion and merger with AIMCO Properties, L.P., a Delaware limited partnership and AIMCO NPI 4 Merger Sub LLC, a Delaware limited liability company of which AIMCO Properties, L.P. is the sole member (the “Merger Subsidiary”), pursuant to which the partnership agreement of the Partnership will first be amended to remove the prohibition on transactions between the Partnership, on the one hand, and its general partner and its affiliates, on the other, following which the Partnership will be converted from a California limited partnership to a Delaware limited partnership named National Property Investors 4, LP (“New NPI 4”), following which the Merger Subsidiary will be merged with and into New NPI 4, with New NPI 4 as the surviving entity. In the conversion and merger, each unit of limited partnership interest (each, a “Unit”) of the Partnership outstanding immediately prior to the consummation of the conversion and merger will be converted into an identical unit of limited partnership interest in New NPI 4 (also known as a “Unit”), following which each Unit (other than Units held by limited partners who perfect their appraisal rights pursuant to the merger agreement) will be converted into the right to receive, at the election of the limited partner, either (i) $195.27 in cash (the “Cash Consideration”) or (ii) a number of partnership common units of AIMCO Properties, L.P. calculated by dividing $195.27 by the average closing price of Aimco common stock, as reported on the New York Stock Exchange, over the ten consecutive trading days ending on the second trading day immediately prior to the effective time of the merger. However, if AIMCO Properties, L.P. determines that the law of the state or other jurisdiction in which a limited partner resides would prohibit the issuance of partnership common units of AIMCO Properties, L.P. in that state or other jurisdiction (or that registration or qualification in that state or jurisdiction would be prohibitively costly), then such limited partner will only be entitled to receive the Cash Consideration for each Unit. Those limited partners who do not make an election will be deemed to have elected to receive the Cash Consideration. In the merger, AIMCO Properties, L.P.’s membership interest in the Merger Subsidiary will be converted into Units of New NPI 4. As a result, after the merger, AIMCO Properties, L.P. will be the sole limited partner of New NPI 4, holding all outstanding Units. NPI Equity Investments, Inc. will continue to be the general partner of New NPI 4 after the conversion and merger, and the Partnership’s partnership agreement in effect immediately prior to the conversion and merger will be the partnership agreement of New NPI 4 after the conversion and merger and will be amended to reflect the conversion and merger. Completion of the conversion and merger is subject to certain conditions, including approval by a majority in interest of the limited partners holding Units. As of June 30, 2011 and December 31, 2010, the Partnership had issued and outstanding 60,005 Units, and AIMCO Properties, L.P. and its affiliates owned 47,850 of those Units, or approximately 79.74% of the number of outstanding Units. Of these 47,850 Units, 26,466 are subject to a voting restriction, which requires such Units to be voted in proportion to the votes cast with respect to the Units not subject to this restriction, which will result in AIMCO Properties, L.P. and its affiliates voting a total of 38,258 Units, or approximately 63.76% of the outstanding Units. AIMCO Properties, L.P. and its affiliates have indicated that they intend to take action by written consent to approve the merger.

Organization, Consolidation and Presentation of Financial Statements

6 Months Ended

Jun. 30, 2011

Organization, Consolidation and Presentation of Financial Statements

Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block]

Note A – Basis of Presentation

The accompanying unaudited financial statements of National Property Investors 4 (the "Partnership" or the "Registrant") have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 8-03 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of NPI Equity Investments, Inc. (“NPI Equity” or the "Managing General Partner"), all adjustments (consisting of normal recurring items) considered necessary for a fair presentation have been included. Operating results for the three and six month periods ended June 30, 2011 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2011. The balance sheet at December 31, 2010 has been derived from the audited financial statements at that date but does not include all of the information and disclosures required by generally accepted accounting principles for complete financial statements. For further information, refer to the financial statements and footnotes thereto included in the Partnership's Annual Report on Form 10-K for the fiscal year ended December 31, 2010. The Managing General Partner is a subsidiary of Apartment Investment and Management Company ("Aimco"), a publicly traded real estate investment trust.

The Partnership’s management evaluated subsequent events through the time this Quarterly Report on Form 10-Q was filed.

Certain reclassifications have been made to the 2010 balances to conform to the 2011 presentation.

On July 28, 2011, the Partnership entered into an agreement and plan of conversion and merger with AIMCO Properties, L.P., a Delaware limited partnership and AIMCO NPI 4 Merger Sub LLC, a Delaware limited liability company of which AIMCO Properties, L.P. is the sole member (the “Merger Subsidiary”), pursuant to which the partnership agreement of the Partnership will first be amended to remove the prohibition on transactions between the Partnership, on the one hand, and its general partner and its affiliates, on the other, following which the Partnership will be converted from a California limited partnership to a Delaware limited partnership named National Property Investors 4, LP (“New NPI 4”), following which the Merger Subsidiary will be merged with and into New NPI 4, with New NPI 4 as the surviving entity.

In the conversion and merger, each unit of limited partnership interest (each, a “Unit”) of the Partnership outstanding immediately prior to the consummation of the conversion and merger will be converted into an identical unit of limited partnership interest in New NPI 4 (also known as a “Unit”), following which each Unit (other than Units held by limited partners who perfect their appraisal rights pursuant to the merger agreement) will be converted into the right to receive, at the election of the limited partner, either (i) $195.27 in cash (the “Cash Consideration”) or (ii) a number of partnership common units of AIMCO Properties, L.P. calculated by dividing $195.27 by the average closing price of Aimco common stock, as reported on the New York Stock Exchange, over the ten consecutive trading days ending on the second trading day immediately prior to the effective time of the merger. However, if AIMCO Properties, L.P. determines that the law of the state or other jurisdiction in which a limited partner resides would prohibit the issuance of partnership common units of AIMCO Properties, L.P. in that state or other jurisdiction (or that registration or qualification in that state or jurisdiction would be prohibitively costly), then such limited partner will only be entitled to receive the Cash Consideration for each Unit. Those limited partners who do not make an election will be deemed to have elected to receive the Cash Consideration.

In the merger, AIMCO Properties, L.P.’s membership interest in the Merger Subsidiary will be converted into Units of New NPI 4. As a result, after the merger, AIMCO Properties, L.P. will be the sole limited partner of New NPI 4, holding all outstanding Units. NPI Equity Investments, Inc. will continue to be the general partner of New NPI 4 after the conversion and merger, and the Partnership’s partnership agreement in effect immediately prior to the conversion and merger will be the partnership agreement of New NPI 4 after the conversion and merger and will be amended to reflect the conversion and merger.

Completion of the conversion and merger is subject to certain conditions, including approval by a majority in interest of the limited partners holding Units. As of June 30, 2011 and December 31, 2010, the Partnership had issued and outstanding 60,005 Units, and AIMCO Properties, L.P. and its affiliates owned 47,850 of those Units, or approximately 79.74% of the number of outstanding Units. Of these 47,850 Units, 26,466 are subject to a voting restriction, which requires such Units to be voted in proportion to the votes cast with respect to the Units not subject to this restriction, which will result in AIMCO Properties, L.P. and its affiliates voting a total of 38,258 Units, or approximately 63.76% of the outstanding Units. AIMCO Properties, L.P. and its affiliates have indicated that they intend to take action by written consent to approve the merger.

- Definition

The entire disclosure for the organization, consolidation and basis of presentation of financial statements disclosure, and significant accounting policies of the reporting entity. May be provided in more than one note to the financial statements, as long as users are provided with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows. Describes procedure if disclosures are provided in more than one note to the financial statements.

+ References+ Details