{"cik":947484,"taxonomy":"us-gaap","tag":"StockholdersEquityNoteStockSplitConversionRatio1","label":"Stockholders' Equity Note, Stock Split, Conversion Ratio","description":"Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.","entityName":"ARCH CAPITAL GROUP LTD.","units":{"pure":[{"start":"2018-05-01","end":"2018-05-31","val":3,"accn":"0000947484-19-000008","fy":2018,"fp":"FY","form":"10-K","filed":"2019-02-28"},{"start":"2018-05-01","end":"2018-05-31","val":3,"accn":"0000947484-20-000012","fy":2019,"fp":"FY","form":"10-K","filed":"2020-02-28"},{"start":"2018-05-01","end":"2018-05-31","val":3,"accn":"0000947484-21-000028","fy":2020,"fp":"FY","form":"10-K","filed":"2021-02-26","frame":"CY2018Q2I"},{"end":"2018-06-18","val":3,"accn":"0000947484-18-000057","fy":2018,"fp":"Q2","form":"10-Q","filed":"2018-08-08"},{"end":"2018-06-18","val":3,"accn":"0000947484-18-000064","fy":2018,"fp":"Q3","form":"10-Q","filed":"2018-11-09"},{"start":"2018-01-01","end":"2018-12-31","val":3,"accn":"0000947484-20-000012","fy":2019,"fp":"FY","form":"10-K","filed":"2020-02-28","frame":"CY2018"}]}}