Financial Instruments and Derivatives Instruments (Details 2) (USD $) In Millions, unless otherwise specified	9 Months Ended
Oct. 02, 2011 year segment M plan week
Reconciliation of changes in fair value of all financial assets and liabilities
Increase in fair value of contingent consideration obligations	$ 0.3
Short-term investments, minimum maturity period for certificates of deposit (in months)	3
Cash equivalents instruments remaining maturities (in months)	three months or less
Percentage of projected intercompany purchases hedged by forward exchange contracts (as a percent)	50.00%
Period of Projected intercompany purchase transactions (in months)	twelve months
Average volume of foreign currency contracts, low end of range	9
Average volume of foreign currency contracts, high end of range	15
Notional amounts of foreign currency purchase contracts	9.0
Contingent consideration
Reconciliation of changes in fair value of all financial assets and liabilities
Balance at the beginning of the period	1.9
Total realized and unrealized (gains) losses included in Earnings	0.3
Balance at the ending of the period	$ 2.2

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate notional amount of all foreign currency derivatives not designated as hedging instruments. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579245-113959

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The increase (decrease) in potential payments under the contingent consideration arrangement.

+ Details

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Namespace Prefix:	wts
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the maximum remaining maturity period at date of purchase of instruments considered as cash equivalents.

+ Details

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Namespace Prefix:	wts
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Balance Type:	na
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- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions.

+ Details

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Namespace Prefix:	wts
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the high end of the range of the average outstanding notional amount of foreign currency derivatives to purchase a foreign currency.

+ Details

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Namespace Prefix:	wts
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the low end of the range of the average outstanding notional amount of foreign currency derivatives to purchase a foreign currency.

+ Details

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Namespace Prefix:	wts
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the percentage of projected intercompany purchase transactions hedged for the next twelve months by forward exchange contracts.

+ Details

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Namespace Prefix:	wts
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum remaining maturity period at date of purchase for certificates of deposit classified as short-term investments.

+ Details

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Namespace Prefix:	wts
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration