Pro Forma Information (Detail) (USD $) In Thousands, except Per Share data	3 Months Ended	9 Months Ended
Oct. 01, 2011	Oct. 02, 2010	Oct. 01, 2011	Oct. 02, 2010
Business Acquisition [Line Items]
Gain on disposal of discontinued operations, net of tax		$ (549)		$ (1,666)
Weighted average common shares outstanding
Basic	98,472	98,298	98,228	98,105
Diluted	99,802	99,514	99,759	99,326
Business Acquisition Pro Forma Information
Business Acquisition [Line Items]
Pro forma net sales	890,546	838,968	2,712,770	2,485,913
Pro forma income from continuing operations	56,287	48,404	181,366	133,122
Gain on disposal of discontinued operations, net of tax		549		1,666
Pro forma net income from continuing operations attributable to Pentair, Inc.	$ 55,325	$ 47,176	$ 177,486	$ 129,528
Pro forma earnings per common share - continuing operations
Basic	$ 0.56	$ 0.48	$ 1.81	$ 1.32
Diluted	$ 0.55	$ 0.47	$ 1.78	$ 1.30
Weighted average common shares outstanding
Basic	98,472	98,298	98,228	98,105
Diluted	99,802	99,514	99,759	99,326

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