v3.26.1
Segment Information - Summary Of Segment Loss And Significant Segment Expenses (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]            
Direct research and development expenses $ 24,729   $ 17,882   $ 47,618 $ 33,201
General and administrative 6,561   3,895   11,581 7,292
Net Income (Loss) (28,935) $ (26,869) (20,191) $ (17,503) (55,804) (37,694)
Operating Segments [Member]            
Segment Reporting [Line Items]            
Other segment items [1] 545   (447)   761 (1,108)
Net Income (Loss) 28,935   20,191   55,804 37,694
Operating Segments [Member] | Location, Statement of Income, Balance [Axis]: us-gaap:OtherGeneralExpense            
Segment Reporting [Line Items]            
General and administrative 1,573   1,080   3,168 2,482
Operating Segments [Member] | Location, Statement of Income, Balance [Axis]: ck0001540171:FacilityExpensesAndInformationTechnology            
Segment Reporting [Line Items]            
Direct research and development expenses 468   386   788 656
General and administrative 528   144   821 291
Operating Segments [Member] | Location, Statement of Income, Balance [Axis]: ck0001540171:PersonnelRelatedExpense            
Segment Reporting [Line Items]            
Direct research and development expenses 3,878   2,907   7,941 5,774
General and administrative 2,542   1,707   4,822 3,166
AP01 | Operating Segments [Member]            
Segment Reporting [Line Items]            
Direct research and development expenses 13,600   12,520   26,755 23,459
AP02 | Operating Segments [Member]            
Segment Reporting [Line Items]            
Direct research and development expenses 4,969   1,372   9,688 2,101
AP03 | Operating Segments [Member]            
Segment Reporting [Line Items]            
Direct research and development expenses $ 832   $ 522   $ 1,060 $ 873
[1] For the three months ended June 30, 2026 and 2025, other segment items consist of $2.5 million and $1.1 million of interest income, respectively, $0.2 million and $0.4 million of accretion of marketable securities, respectively, $2.8 million and $1.1 million of stock-based compensation expense, respectively, $0.3 million and zero of interest expense, respectively, and $178 thousand and $50 thousand of depreciation expense and other expenses, respectively. For the six months ended June 30, 2026 and 2025, other segment items consist of $3.4 million and $1.8 million of interest income, respectively, $0.4 million and $1.0 million accretion of marketable securities, respectively, $4.0 million and $1.7 million
of stock-based compensation expense, respectively, $0.4 million and zero of interest expense, respectively, and $228 thousand and $94 thousand of depreciation expense and other expenses, respectively.