Description of Business and Significant Accounting Policies (Narrative) (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Oct. 03, 2015 USD ($)	Oct. 03, 2015 USD ($)
Basis Of Presentation Fiscal Year End And New Accounting Pronouncements Disclosure [Abstract]
Operating Cycle		The fiscal year of the Company consists of a 52- or 53-week period ending on the Saturday closest to December 31. Fiscal year 2015 is a 52-week period ending on January 2, 2016, with quarterly periods ending on April 4, July 4 and October 3, 2015, while fiscal year 2014 was a 53-week period ending on January 3, 2015, with quarterly periods ending on April 5, July 5 and October 4, 2014.
Year Founded		1973
Opta Minerals Inc [Member]
Noncontrolling Interest [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	66.00%	66.00%
Line Of Credit Facility Covenant Compliance	As described in note 1, as at June 30, 2015 and September 30, 2015, Opta Minerals was not in compliance with all of its financial covenants under its credit agreement. Failure to meet a financial covenant constitutes an event of default, unless the lenders agree to a waiver or amendment. On August 11, 2015, in respect of the June 30, 2015 default and October 30, 2015, in respect of the September 30, 2015 default, Opta Minerals obtained waivers in respect of the aforementioned covenant requirements from its lenders, provided that Opta Minerals meets certain additional financial covenants. As there is no assurance that Opta Minerals will be in compliance with all its financial covenants at all measurement dates within the next 12 months, the non-revolving term credit facility has been classified as current on the consolidated balance sheet as at October 3, 2015.	Over the last several years, Opta Minerals has periodically breached certain financial covenants under its credit agreement with a syndicate of lenders, including as at June 30, 2015 and September 30, 2015. As described in note 7, Opta Minerals obtained waivers from the lenders on August 11, 2015 in respect of the June 30, 2015 default and October 30, 2015, in respect of the September 30, 2015 default. In connection with these waivers, certain additional covenants were added from the date of the waivers through November 30, 2015. In addition, the lenders agreed to extend the maturity of Opta Minerals’ revolving term credit facility to November 30, 2015. Opta Minerals will require the continued support of its current financial lenders and, effective November 30, 2015, Opta Minerals will require another extension of its revolver and an additional waiver on future covenants, if breached, or an alternative source of financing. There can be no assurance that a further extension and additional waiver will be provided or that alternative sources of financing on terms favorable to Opta Minerals could be obtained to finance its operations and meet its obligations.
Carrying Value Of Investment In Subsidiary	$ 25,000	$ 25,000
Carrying Value of Investment In Subsidiary - Additional Information		Opta Minerals ability to continue to operate as a going concern could also have a significant impact on the Company’s ability to recover the carrying value of its investment in Opta Minerals, which amounted to approximately $25,000 as at October 3, 2015.