Intangible assets, other than goodwill, consisted of the following as of March 31, 2024 and December 31, 2023, respectively: | | | | | | | | | | | | | | | | | | | | | | | | | (in millions) | Gross Carrying Amount | | Accumulated Amortization | | Net | | Weighted Average Amortization Period in Years | | Intangible assets subject to amortization: | | | | | | | | | Customer relationships | $ | 287.6 | | | $ | (117.5) | | | $ | 170.1 | | | 14.5 | | Acquired technology | 330.8 | | | (217.9) | | | 112.9 | | | 6.3 | | Brand portfolio | 11.5 | | | (7.7) | | | 3.8 | | | 7.8 | | Total intangible assets subject to amortization | $ | 629.9 | | | $ | (343.1) | | | $ | 286.8 | | | | | | | | | | | | | Intangible assets not subject to amortization | | | | | | | | | Pre-Acquisition ZI brand portfolio | $ | 33.0 | | | $ | — | | | $ | 33.0 | | | | | Total intangible assets not subject to amortization | $ | 33.0 | | | $ | — | | | $ | 33.0 | | | | | | | | | | | | | Total intangible assets | $ | 662.9 | | | $ | (343.1) | | | $ | 319.8 | | | |
| | | | | | | | | | | | | | | | | | | | | | | | | (in millions) | Gross Carrying Amount | | Accumulated Amortization | | Net | | Weighted Average Amortization Period in Years | | Intangible assets subject to amortization: | | | | | | | | | Customer relationships | $ | 287.6 | | | $ | (112.5) | | | $ | 175.1 | | | 14.5 | | Acquired technology | 330.8 | | | (208.4) | | | 122.4 | | | 6.3 | | Brand portfolio | 11.5 | | | (7.4) | | | 4.1 | | | 7.9 | Total intangible assets subject to amortization | $ | 629.9 | | | $ | (328.3) | | | $ | 301.6 | | | | | | | | | | | | Intangible assets not subject to amortization: | | | | | | | | | Pre-Acquisition ZI brand portfolio | $ | 33.0 | | | $ | — | | | $ | 33.0 | | | | Total intangible assets not subject to amortization | $ | 33.0 | | | $ | — | | | $ | 33.0 | | | | | | | | | | | | | Total intangible assets | $ | 662.9 | | | $ | (328.3) | | | $ | 334.6 | | | |
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