Fair Value Measurements (Details) - USD ($) $ in Thousands	6 Months Ended
	Jul. 04, 2015	Dec. 31, 2014
Assets:
Held-to-maturity Securities, Transferred Security, at Carrying Value	$ 0
Held-to-maturity Securities, Unrecognized Holding Gain	0
Other than Temporary Impairment Losses, Investments, Held-to-maturity Securities	0
Assets held in rabbi trusts	39,008	$ 40,270
Available for sale securities	4,697	15,432
Fair Value Assets	43,705	55,702
Liabilities:
Embedded derivative	(1,387)	(1,105)
Fair Value Liabilities	(1,387)	(1,105)
Long-term Debt, Fair Value	726,400	853,500
Carrying value of long-term debt, excluding derivative liabilities	425,907	453,817
Derivative, Notional Amount	$ 14,000
Derivative, Description of Terms	In the third fiscal quarter of 2014, the Company entered into a forward contract with a highly-rated financial institution to mitigate the foreign currency risk associated with an intercompany loan denominated in a currency other than the legal entity's functional currency. The notional amount of the forward contract was $14,000 as of July 4, 2015. The intercompany loan was used to finance a portion of the purchase price for Capella. The forward contract settles monthly and is expected to be renewed at the Company's discretion on a monthly basis until the intercompany loan is repaid. The forward contract was renewed on the last day of the second fiscal quarter. We have not designated the forward contract as a hedge for accounting purposes, and as such the change in the fair value of the contract is recognized in the consolidated condensed statements of operations as a component of other income (expense).
Fair Value, Inputs, Level 1 [Member]
Assets:
Assets held in rabbi trusts	$ 25,382	26,853
Available for sale securities	3,965	4,439
Fair Value Assets	29,347	31,292
Liabilities:
Fair Value Liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Assets held in rabbi trusts	13,626	13,417
Available for sale securities	732	10,993
Fair Value Assets	14,358	24,410
Liabilities:
Fair Value Liabilities	0	0
Fair Value, Inputs, Level 3 [Member]
Assets:
Assets held in rabbi trusts	0	0
Available for sale securities	0	0
Fair Value Assets	0	0
Liabilities:
Fair Value Liabilities	(1,387)	(1,105)
Convertible Senior Debentures, Due 2040 [Member]
Liabilities:
Embedded derivative	(632)	(526)
Convertible Senior Debentures, Due 2040 [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures, Due 2040 [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures, Due 2040 [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Embedded derivative	(632)	(526)
Convertible Senior Debentures, Due 2041 [Member]
Liabilities:
Embedded derivative	(478)	(341)
Convertible Senior Debentures, Due 2041 [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures, Due 2041 [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures, Due 2041 [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Embedded derivative	(478)	(341)
Convertible Senior Debentures, Due 2042 [Member]
Liabilities:
Embedded derivative	(277)	(238)
Convertible Senior Debentures, Due 2042 [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures, Due 2042 [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures, Due 2042 [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Embedded derivative	$ (277)	$ (238)