Commitments and Contingencies (Details)			6 Months Ended
	Jul. 26, 2016 USD ($) item	Jul. 06, 2016 USD ($)	Jul. 28, 2017 USD ($) store	Jul. 29, 2016 USD ($)	Apr. 28, 2017 USD ($)	Jan. 27, 2017 USD ($)	Mar. 30, 2016 item
Commitments and contingencies
Estimated workers' compensation claims			$ 68,941,000			$ 69,169,000
Net proceeds from sale-leaseback transactions			15,317,000	$ 31,503,000
Warehouse Facility
Commitments and contingencies
Carrying value		$ 12,100,000
Net proceeds from sale-leaseback transactions		28,500,000
Escrow deposit amount		$ 1,000,000
Amount received from deposit held in escrow						600,000
Finance lease obligation						30,100,000
Warehouse Facility | Selling, general and administrative expenses
Commitments and contingencies
Gain on sale recorded					$ 18,500,000
Mid-Term Cash Incentive Plan
Commitments and contingencies
Percentage of participant's award eligible for payment based on initial EBITDA achievement	50.00%
Amount paid under the incentive plan	$ 0
Percentage of participant's award eligible for payment based on subsequent EBITDA achievement	50.00%
Maximum payout under the incentive plan	$ 22,500,000
Amount accrued under the incentive plan			11,900,000			6,000,000
Special Bonus Letters
Commitments and contingencies
Number of executives approved for special bonus letters | item	3
Number of days within which executives eligible to receive special bonus after the refinancing transaction	30 days
Total amount of special bonuses to be earned by the executives	$ 4,000,000
Amount accrued under the special bonus letters			0
Health Insurance
Commitments and contingencies
Self Insured Health Insurance Liability			$ 900,000			900,000
Wage and Hour Matters | Shelley Pickett v. 99 Cents Only Stores
Commitments and contingencies
Number of stores where the named plaintiffs worked | store			2
Wage and Hour Matters | Shelley Pickett v. 99 Cents Only Stores | Minimum
Commitments and contingencies
Civil penalties per violation, per each pay period for each affected employee			$ 100
Wage and Hour Matters | Shelley Pickett v. 99 Cents Only Stores | Maximum
Commitments and contingencies
Civil penalties per violation, per each pay period for each affected employee			200
Wage and Hour Matters | Phillip Clavel v. 99 Cents Only Stores
Commitments and contingencies
Number of periods of employment | item							2
California | Workers' Compensation
Commitments and contingencies
Estimated workers' compensation claims			68,900,000			69,100,000
Texas | Workers' Compensation | Maximum
Commitments and contingencies
Estimated workers' compensation claims			$ 100,000			$ 100,000