Note 4 - Fair Values of Assets and Liabilities (Details Textual) $ in Millions	12 Months Ended
Feb. 03, 2018 USD ($)
Proceeds from Sale of Other Investments	$ 2.2
Gain on Sale, Net of Impairment, of Privately Held Investments, Net	$ 0.2

This item represents the gain on the sale of privately held investments net of other than temporary declines in value that have been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment net of gain on sale of privately held investments, net.

No definition available.

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Namespace Prefix:	sigm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration