Fair value measurement - Fair Value of Pension Plan Assets by Level within Fair Value Hierarchy (Detail) - USD ($) $ in Thousands | Dec. 27, 2015 | Dec. 28, 2014 | Dec. 29, 2013 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | $ 2,541,396 | $ 2,648,167 | |
Fair value of pension plan liabilities | (2,623) | (4,268) | |
Cash and other | 19,854 | 10,990 | |
Total net fair value of plan assets | 2,558,627 | 2,654,889 | |
U.S. government-related securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 3,744 | |
Mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 3,824 | |
Other government bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 4,266 | |
Corporate bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 1,275 | 23,384 | |
Corporate stock | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 769,597 | 866,418 | |
Real estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 126,049 | 118,936 | |
Equities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 549,159 | 693,277 | |
Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 493,661 | 223,321 | |
Interest in reg. invest. companies | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 138,791 | 188,566 | |
Interest in 103-12 investments | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 22,776 | |
Partnership/joint venture interests | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 131,663 | 162,458 | |
Hedge funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 331,044 | 334,250 | |
Derivative contracts | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 157 | 2,947 | |
Derivative liabilities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of pension plan liabilities | (2,623) | (4,268) | |
Level 1 | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 872,786 | 1,017,171 | |
Fair value of pension plan liabilities | 0 | (4) | |
Cash and other | 14,938 | 8,546 | |
Total net fair value of plan assets | 887,724 | 1,025,713 | |
Level 1 | U.S. government-related securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 1 | Mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 1 | Other government bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 1 | Corporate bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 1 | Corporate stock | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 769,597 | 866,418 | |
Level 1 | Real estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 1 | Equities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 1 | Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 2,478 | 6,593 | |
Level 1 | Interest in reg. invest. companies | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 100,711 | 144,160 | |
Level 1 | Interest in 103-12 investments | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 1 | Partnership/joint venture interests | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 1 | Hedge funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 1 | Derivative contracts | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 1 | Derivative liabilities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of pension plan liabilities | 0 | (4) | |
Level 2 | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 1,127,680 | 1,069,100 | |
Fair value of pension plan liabilities | (615) | (2,387) | |
Cash and other | 4,916 | 2,444 | |
Total net fair value of plan assets | 1,131,981 | 1,069,157 | |
Level 2 | U.S. government-related securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 3,744 | |
Level 2 | Mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 3,735 | |
Level 2 | Other government bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 4,266 | |
Level 2 | Corporate bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 1,275 | 23,027 | |
Level 2 | Corporate stock | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 2 | Real estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 2 | Equities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 549,159 | 693,277 | |
Level 2 | Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 491,183 | 216,728 | |
Level 2 | Interest in reg. invest. companies | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 38,080 | 44,406 | |
Level 2 | Interest in 103-12 investments | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 22,776 | |
Level 2 | Partnership/joint venture interests | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 27,412 | 34,144 | |
Level 2 | Hedge funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 20,454 | 20,166 | |
Level 2 | Derivative contracts | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 117 | 2,831 | |
Level 2 | Derivative liabilities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of pension plan liabilities | (615) | (2,387) | |
Level 3 | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 540,930 | 561,896 | $ 478,072 |
Fair value of pension plan liabilities | (2,008) | (1,877) | |
Cash and other | 0 | 0 | |
Total net fair value of plan assets | 538,922 | 560,019 | |
Level 3 | U.S. government-related securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 3 | Mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 89 | 372 |
Level 3 | Other government bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 3 | Corporate bonds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 357 | 800 |
Level 3 | Corporate stock | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 3 | Real estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 126,049 | 118,936 | 105,875 |
Level 3 | Equities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 3 | Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 3 | Interest in reg. invest. companies | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Level 3 | Interest in 103-12 investments | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | | 0 | |
Level 3 | Partnership/joint venture interests | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 104,251 | 128,314 | 131,868 |
Level 3 | Hedge funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 310,590 | 314,084 | 239,004 |
Level 3 | Derivative contracts | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of plan assets | 40 | 116 | 153 |
Level 3 | Derivative liabilities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Fair value of pension plan liabilities | $ (2,008) | $ (1,877) | $ (1,877) |