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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.

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