Summary of Significant Accounting Policies (Details) (USD $)	3 Months Ended
	Mar. 31, 2013
Limited Partnership Distributions [Line Items]
Impairment of real estate	$ 0
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-Q