Postretirement Medical Benefits - Change in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Feb. 01, 2020	Feb. 02, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 202,084	$ 1,029,857
Ending balance	54,344	202,084
AOCI, defined benefit plan adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(3,658)	(3,331)
Ending balance	(2,282)	(3,658)
Net prior service credit amortization
Accumulated Other Comprehensive Income (Loss) [Line Items]
Current period activity	693	693
Amortization of net actuarial gain
Accumulated Other Comprehensive Income (Loss) [Line Items]
Current period activity	962	316
Net actuarial loss for the period
Accumulated Other Comprehensive Income (Loss) [Line Items]
Current period activity	$ (279)	$ (1,336)