EMPLOYEE BENEFITS - Investmt assets (Details) - Pension plan $ in Thousands		12 Months Ended
	Jan. 14, 2011 item	Dec. 27, 2015 USD ($) item	Dec. 28, 2014 USD ($)
Changes in the fair value of the plan's Level 3 investment assets
Fair value of plan assets, beginning of year		$ 1,478,686
Fair value of plan assets, end of year		1,340,600	$ 1,478,686
Additional disclosures on plan assets
Number of locations from which properties were contributed | item	7
Level 3
Changes in the fair value of the plan's Level 3 investment assets
Fair value of plan assets, beginning of year		54,215	59,432
Purchases, issuances, sales, settlements			(3,312)
Realized gains		2,479	(12,180)
Transfer in or out of level 3		(3,936)	(4,456)
Unrealized gains		4,884	14,731
Fair value of plan assets, end of year		57,642	54,215
Real estate | Level 3
Changes in the fair value of the plan's Level 3 investment assets
Fair value of plan assets, beginning of year		47,579	52,265
Purchases, issuances, sales, settlements			(3,312)
Realized gains		2,479	3,973
Transfer in or out of level 3		(3,936)	(3,973)
Unrealized gains		4,238	(1,374)
Fair value of plan assets, end of year		$ 50,360	47,579
Private Equity
Additional disclosures on plan assets
Number of funds closed out | item		2
Private Equity | Level 3
Changes in the fair value of the plan's Level 3 investment assets
Fair value of plan assets, beginning of year		$ 6,636	7,167
Realized gains			(16,153)
Transfer in or out of level 3			(483)
Unrealized gains		646	16,105
Fair value of plan assets, end of year		$ 7,282	$ 6,636