Pension, Postretirement and Postemployment Benefits, Beginning of Fair Value Measurement (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 25, 2016
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	$ 383,000	$ 309,300
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	134,500	127,400
Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Large Cap [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	38,400	29,100
Equity - Large Cap [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	38,400	29,100
Equity - Large Cap [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Large Cap [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Small Cap [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	25,300	29,200
Equity - Small Cap [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	25,300	29,200
Equity - Small Cap [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Small Cap [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - International [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	43,900	40,100
Equity - International [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	43,900	40,100
Equity - International [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - International [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Other [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	300	1,300
Equity - Other [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Other [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Equity - Other [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Fixed Income Funds [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	217,200	119,500
Fixed Income Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Fixed Income Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Fixed Income Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Total Return Fund [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	26,900	29,000
Total Return Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	26,900	29,000
Total Return Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Total Return Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Cash Equivalents [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	31,000	61,100
Cash Equivalents [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	0	0
Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair values of plan assets by asset class and fair value hierarchy level [Abstract]
Fair Value of Plan Asset	$ 0	$ 0