Summary of Significant Accounting Policies (Details)	12 Months Ended
Summary of Significant Accounting Policies (Details)	Dec. 31, 2012
Cash Preferred Units
Allocations of Net Income, Net Loss, and Gain on Sale
Distribution of excess net income based on allocation (percent)	99.00%
Tax Preferred Units
Allocations of Net Income, Net Loss, and Gain on Sale
Distribution of net loss, depreciation, and amortization based on allocation (percent)	99.00%
General Partners
Allocations of Net Income, Net Loss, and Gain on Sale
Distribution of excess net income based on allocation (percent)	1.00%
Distribution of net loss, depreciation, and amortization based on allocation (percent)	1.00%
First Priority \| Cash Preferred Units
Distribution of Net Cash from Operations
Distribution of net cash from operations based on capital contributions (percent)	10.00%
Second Priority \| General Partners
Distribution of Net Cash from Operations
Distribution of net cash from operations based on cumulative distributions (percent)	10.00%
Third Priority \| Cash Preferred Units
Distribution of Net Cash from Operations
Distribution of net cash from operations based on allocation (percent)	90.00%
Third Priority \| General Partners
Distribution of Net Cash from Operations
Distribution of net cash from operations based on allocation (percent)	10.00%
Third Priority \| Limited Partners
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on partner capital contributions (percent)	100.00%
Fourth Priority \| Limited Partners
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on partners' return on capital contributions (percent)	10.00%
Fifth Priority \| Cash Preferred Units
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on preferential limited partner return (percent)	10.00%
Fifth Priority \| Tax Preferred Units
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on preferential limited partner return (percent)	15.00%
Sixth Priority \| General Partners
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on partner capital contributions (percent)	100.00%
Seventh Priority \| General Partners
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based additional excess distributions (percent)	20.00%
Eighth Priority \| General Partners
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on allocation (percent)	20.00%
Eighth Priority \| Limited Partners
Distribution of Net Sale Proceeds
Distribution of net sale proceeds based on allocation (percent)	80.00%

WELLS REAL ESTATE FUND XII LP 10-K