Shareholders' Equity - Narrative (Details) $ / shares in Units, $ in Millions			4 Months Ended	12 Months Ended
	Dec. 28, 2025 shares	Sep. 15, 2025 USD ($) $ / shares shares	Dec. 31, 2025 shares	Dec. 31, 2025 vote shares	Sep. 11, 2025 shares
Class of Stock [Line Items]
Common stock to LLC unit ratio			1	1
LLC units outstanding					50,055,807
Offering cost | $		$ 8.0
Stock Transfered During Period, Shares	539,019
Black Rock OpCo
Class of Stock [Line Items]
LLC units outstanding			17,478,452	17,478,452
Economic interest			34.90%	34.90%
LLC Units held by Black Rock Coffee Bar, Inc.
Class of Stock [Line Items]
LLC units outstanding					17,478,452
Continuing Equity Owners
Class of Stock [Line Items]
LLC units outstanding			32,577,355	32,577,355	32,577,355
Voting Percentage			92.90%	92.90%
Black Rock OpCo | LLC Units held by Black Rock Coffee Bar, Inc. | LLC Units
Class of Stock [Line Items]
Sale of stock (in shares)		3,857,642
Net proceeds from IPO | $		$ 71.8
Continuing Equity Owners | Black Rock OpCo
Class of Stock [Line Items]
Economic interest			65.10%	65.10%
Common stock units subject to time based requirements (in shares)				80,500
Continuing Equity Owners | LLC Units
Class of Stock [Line Items]
Sale of stock (in shares)		13,054,122
Net proceeds from IPO | $		$ 242.8
IPO
Class of Stock [Line Items]
Sale of stock (in shares)		16,911,764
Public offering price | $ / shares		$ 20.00
Issuance of common stock | $		$ 314.6
Net proceeds from IPO | $		$ 306.5
Over-Allotment Option
Class of Stock [Line Items]
Sale of stock (in shares)		2,205,882
Class A Common stock
Class of Stock [Line Items]
Number of votes per share | vote				1
Shares outstanding (in shares)			17,478,452	17,478,452
Voting Percentage			7.10%	7.10%
Class B Common stock
Class of Stock [Line Items]
Number of votes per share | vote				1
Shares outstanding (in shares)			10,916,155	10,916,155
Class B Common stock | Common Stock
Class of Stock [Line Items]
LLC units and class c common stock (in shares)	539,019		539,000
Class C Common stock
Class of Stock [Line Items]
Number of votes per share | vote				10
Shares outstanding (in shares)			21,661,200	21,661,200
Class C Common stock | Common Stock
Class of Stock [Line Items]
LLC units and class c common stock (in shares)			(539,000)