Pension Benefits - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 25, 2016	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Pension Benefits
Pension settlement expense			$ 0	$ 102,109	$ 21,294
Pension Plan [Member]
Pension Benefits
Service cost			10,065	9,799	9,134
Interest cost			60,153	68,582	74,465
Expected return on plan assets			(82,327)	(102,900)	(111,159)
Amortization and other costs			31,916	33,369	32,458
Amortization of prior service credit			(1,945)	(1,945)	(1,945)
Effect of settlement/curtailment			221	102,109	19,695
Net periodic pension cost			18,083	109,014	22,648
Reduction in pension benefit obligation	$ 263,300	$ 52,200
Pension settlement expense	102,100	21,300
Discretionary contributions to pension plans	$ 120,000
Lump-sum payments made from Company cash		49,500
Curtailment		$ 1,700
Qualified Plan [Member] | Pension Plan [Member]
Pension Benefits
Service cost			9,986	9,720	8,991
Interest cost			52,770	60,742	66,293
Expected return on plan assets			(82,327)	(102,900)	(111,159)
Amortization and other costs			26,802	29,051	28,274
Amortization of prior service credit			(1,945)	(1,945)	(1,945)
Effect of settlement/curtailment			0	102,109	21,294
Net periodic pension cost			5,286	96,777	11,748
Pension contributions			8,400
Nonqualified Plan [Member] | Pension Plan [Member]
Pension Benefits
Service cost			79	79	143
Interest cost			7,383	7,840	8,172
Expected return on plan assets			0	0	0
Amortization and other costs			5,114	4,318	4,184
Amortization of prior service credit			0	0	0
Effect of settlement/curtailment			221	0	(1,599)
Net periodic pension cost			$ 12,797	$ 12,237	$ 10,900