| Document and Entity Information | Nov. 18, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 18, 2020 |
| Entity Registrant Name | PC Connection, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 0-23827 |
| Entity Tax Identification Number | 02-0513618 |
| Entity Address, Address Line One | 730 Milford Road |
| Entity Address, City or Town | Merrimack |
| Entity Address, State or Province | NH |
| Entity Address, Postal Zip Code | 03054 |
| City Area Code | 603 |
| Local Phone Number | 683-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001050377 |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | CNXN |
| Security Exchange Name | NASDAQ |
