Document and Entity Information
3 Months Ended
Mar. 31, 2019
Document And Entity Information [Abstract]  
Document Type 6-K
Amendment Flag false
Document Period End Date Mar. 31, 2019
Document Fiscal Year Focus 2019
Document Fiscal Period Focus Q1
Trading Symbol ICLR
Entity Registrant Name ICON PLC
Entity Central Index Key 0001060955
Current Fiscal Year End Date --12-31