| Cover - shares | 6 Months Ended | |
| Jun. 30, 2021 | Aug. 31, 2021 | |
| Document Information [Line Items] | ||
| Document Type | 10-Q/A | |
| Amendment Flag | true | |
| Amendment Description | Amendment No. 1 | |
| Document Quarterly Report | true | |
| Document Transition Report | false | |
| Document Period End Date | Jun. 30, 2021 | |
| Document Fiscal Period Focus | Q2 | |
| Document Fiscal Year Focus | 2021 | |
| Current Fiscal Year End Date | --12-31 | |
| Entity File Number | 001-39362 | |
| Entity Registrant Name | CAPSTAR SPECIAL PURPOSE ACQUISITION CORP. | |
| Entity Central Index Key | 0001805087 | |
| Entity Tax Identification Number | 84-4730610 | |
| Entity Incorporation, State or Country Code | DE | |
| Entity Address, Address Line One | 405 West 14th Street | |
| Entity Address, City or Town | Austin | |
| Entity Address, State or Province | TX | |
| Entity Address, Postal Zip Code | 78701 | |
| City Area Code | 512 | |
| Local Phone Number | 340-7800 | |
| Entity Current Reporting Status | No | |
| Entity Interactive Data Current | Yes | |
| Entity Filer Category | Non-accelerated Filer | |
| Entity Small Business | true | |
| Entity Emerging Growth Company | true | |
| Elected Not To Use the Extended Transition Period | false | |
| Entity Shell Company | true | |
| Units, each consisting of one share of Class A Common Stock and one-half of one Warrant | ||
| Document Information [Line Items] | ||
| Title of 12(b) Security | Units, each consisting of one share of Class A Common Stock and one-half of one Warrant | |
| Trading Symbol | CPSR.U | |
| Security Exchange Name | NYSE | |
| Class A common stock | ||
| Document Information [Line Items] | ||
| Title of 12(b) Security | Class A Common Stock, par value $0.0001 per share | |
| Trading Symbol | CPSR | |
| Security Exchange Name | NYSE | |
| Entity Common Stock, Shares Outstanding | 27,600,000 | |
| Warrants, each whole warrant exercisable for one share of Class A Common Stock at an exercise price of $11.50 | ||
| Document Information [Line Items] | ||
| Title of 12(b) Security | Warrants, each whole warrant exercisable for one share of Class A Common Stock at an exercise price of $11.50 | |
| Trading Symbol | CPSR WS | |
| Security Exchange Name | NYSE | |
| Class B common stock | ||
| Document Information [Line Items] | ||
| Entity Common Stock, Shares Outstanding | 6,900,000 |
