SIGNIFICANT ACCOUNTING POLICIES - AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 24, 2017	Sep. 30, 2018	Sep. 24, 2017
Changes in stockholders' equity
Balance at the beginning of the period			$ (449,369)
Amounts reclassified from AOCL			16,649
Other comprehensive income	$ 5,550	$ 10,409	16,649	$ 19,596
Balance at the end of the period	(432,720)		(432,720)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Retirement benefit expense	2,778	3,328	8,335	9,983
Minimum Pension and Post-Retirement Liability
Changes in stockholders' equity
Balance at the beginning of the period			(442,406)
Amounts reclassified from AOCL			16,649
Other comprehensive income			16,649
Balance at the end of the period	(425,757)		(425,757)
Minimum Pension and Post-Retirement Liability | Amount Reclassified from AOCI
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Retirement benefit expense	5,550	$ 7,712	16,649	$ 12,853
Other Comprehensive Loss Related to Equity Investments
Changes in stockholders' equity
Balance at the beginning of the period			(6,963)
Balance at the end of the period	$ (6,963)		$ (6,963)