Benefit Plans, Pension Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 26, 2015
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 169,140		$ 176,077
Approximate percentage of common stock invested in major industry	90.00%		89.00%
Approximate percentage of mutual funds actively managed	68.00%		67.00%
Approximate percentage of indexed mutual funds	32.00%		33.00%
Percentage of mutual funds' assets that are invested in U.S equities	5.00%		12.00%
Percent of mutual funds' assets that are invested in non-U.S. equities	38.00%		38.00%
Percent of mutual funds assets invested in US fixed income securities	54.00%		46.00%
Percent of mutual funds' assets that are invested in non-U.S. fixed income securities	3.00%		4.00%
Cash and Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 4,245		$ 16,632
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	18,601	[1]	25,229	[2]
Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	141,599	[3]	129,626	[4]
Limited Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	4,695		4,590
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	28,418		51,527
Level 1 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	4,245		16,632
Level 1 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	18,601	[1]	25,229	[2]
Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	5,572	[3]	9,666	[4]
Level 1 [Member] | Limited Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0		0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	136,027		119,960
Level 2 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0		0
Level 2 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	[1]	0	[2]
Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	136,027	[3]	119,960	[4]
Level 2 [Member] | Limited Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0		0
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	4,695		4,590
Level 3 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0		0
Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	[1]	0	[2]
Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	[3]	0	[4]
Level 3 [Member] | Limited Partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 4,695		$ 4,590
Pension Benefits [Member]
Asset category [Abstract]
Total plan assets	100.00%		100.00%
Expected long-term rate of return on plan assets	5.56%		5.59%
Pension Benefits [Member] | Equity Securities [Member]
Asset category [Abstract]
Total plan assets	47.00%		51.00%
Pension Benefits [Member] | Fixed Income Securities [Member]
Asset category [Abstract]
Total plan assets	48.00%		37.00%
Pension Benefits [Member] | Cash and Money Market Funds [Member]
Asset category [Abstract]
Total plan assets	3.00%		9.00%
Pension Benefits [Member] | Alternative Investments [Member]
Asset category [Abstract]
Total plan assets	2.00%		3.00%
Pension Benefits [Member] | Minimum [Member] | Fixed Income Securities [Member]
Asset category [Abstract]
Total plan assets	60.00%
Pension Benefits [Member] | Maximum [Member] | Equity Securities [Member]
Asset category [Abstract]
Total plan assets	30.00%
Pension Benefits [Member] | Maximum [Member] | Alternative Investments [Member]
Asset category [Abstract]
Total plan assets	5.00%
Limited Partnerships [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 4,590
Redemptions	(196)
Subscriptions	196
Net appreciation in fair value	105
Ending balance	$ 4,695		$ 4,590

[1] Approximately 90 percent of common stock represents investments in U.S. companies primarily in the health care, utilities, financials, consumer staples, industrials, and information technology sectors. All investments in common stock are listed on U.S. stock exchanges.

[2] Approximately 89 percent of common stock represents investments in U.S. companies primarily in the health care, utilities, financials, consumer staples, industrials, and information technology sectors. All investments in common stock are listed on U.S. stock exchanges.

[3] Approximately 68 percent of mutual funds are actively managed funds and approximately 32 percent of mutual funds are index funds. Additionally, five percent of the mutual funds' assets are invested in U.S. equities, 38 percent in non-U.S. equities, 54 percent in U.S. fixed income securities, and three percent in non-U.S. fixed income securities.

[4] Approximately 67 percent of mutual funds are actively managed funds and approximately 33 percent of mutual funds are index funds. Additionally, 12 percent of the mutual funds' assets are invested in U.S. equities, 38 percent in non-U.S. equities, 46 percent in U.S. fixed income securities, and 4 percent in non-U.S. fixed income securities.