Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 28, 2014	Dec. 31, 2013
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	38,721	36,992
Available for sale securities	7,568	7,356
Fair Value Assets	46,289	44,348
Liabilities:
Embedded derivative	(999)	(1,037)
Fair Value Liabilities	(999)	(1,037)
Long-term Debt, Fair Value	846,900	750,700
Carrying value of long-term debt, excluding derivative liabilities	385,807	363,874
Fair Value, Inputs, Level 1 [Member]
Assets:
Assets held in rabbi trusts	25,351	24,064
Available for sale securities	7,568	7,356
Fair Value Assets	32,919	31,420
Liabilities:
Fair Value Liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Assets held in rabbi trusts	13,370	12,928
Available for sale securities	0	0
Fair Value Assets	13,370	12,928
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	(999)	(1,037)
Convertible Senior Debentures 2040 [Member]
Liabilities:
Embedded derivative	(460)	(491)
Convertible Senior Debentures 2040 [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures 2040 [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures 2040 [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Embedded derivative	(460)	(491)
Convertible Senior Debentures 2041 [Member]
Liabilities:
Embedded derivative	(343)	(349)
Convertible Senior Debentures 2041 [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures 2041 [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures 2041 [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Embedded derivative	(343)	(349)
Convertible Senior Debentures 2042 [Member]
Liabilities:
Embedded derivative	(196)	(197)
Convertible Senior Debentures 2042 [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures 2042 [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities:
Embedded derivative	0	0
Convertible Senior Debentures 2042 [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Embedded derivative	$ (196)	$ (197)