Summary of Significant Accounting Policies - Revenue Recognition and Related, and Advertising Costs (Details) - USD ($)	12 Months Ended
	Feb. 01, 2020	Feb. 02, 2019	Feb. 03, 2018
Accounting Policies [Abstract]
Deferred revenue, remaining performance obligations	$ 14,800,000	$ 13,400,000
Significant Accounting Policies [Line Items]
Percentage of cash back earned (up to)	2.00%
Maximum annual cash back amount	$ 500
Cash back in form of electronic awards issued	$ 20
Cash back in form of electronic awards issued, expiration term	6 months
Other current liabilities	$ 26,700,000	25,800,000
Sales returns reserve	$ 6,500,000	$ 6,800,000	$ 1,500,000
Advertising expenses as a percent of net sales	0.60%	0.70%	0.60%
My BJ's Perks Mastercard
Significant Accounting Policies [Line Items]
Percentage of cash back earned (up to)	5.00%
Card outside of BJ's
Significant Accounting Policies [Line Items]
Percentage of cash back earned (up to)	2.00%
Membership
Significant Accounting Policies [Line Items]
Membership term	12 months
Deferred revenue	$ 144,000,000	$ 134,400,000
Revenue recognized	302,151,000	282,893,000
Gift Card Programs
Significant Accounting Policies [Line Items]
Deferred revenue	10,300,000	9,100,000
Revenue recognized	49,100,000	$ 50,000,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-02-02
Accounting Policies [Abstract]
Deferred revenue, remaining performance obligations	$ 12,500,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred revenue, remaining performance obligations, period of recognition	1 year
Net sales | Revenue from rights concentration risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	96.00%
Revenues | Revenue from rights concentration risk
Significant Accounting Policies [Line Items]
Concentration risk percentage	93.00%