4. Goodwill and Intangible Assets

The following table presents the changes in our goodwill balance (in thousands):

 

The change in goodwill in 2016 is attributable to the acquisition of Other Art Fairs Ltd, which operates as The Other Art Fair, in July 2016. See Note 11 for additional information. Goodwill is tested at the reporting unit level and as of September 30, 2016, we have two reporting units: marketplaces and content and media. As of September 30, 2016, our goodwill balance related entirely to our marketplaces reporting unit.

Intangible assets consisted of the following (in thousands):

 

 

 

 

Identifiable finite-lived intangible assets are amortized on a straight-line basis over their estimated useful lives commencing on the date that the asset is available for its intended use.

Total amortization expense for the periods shown below includes (in thousands):

 

Service costs include accelerated amortization charges of $1.2 million and $0.1 million for the three months ended September 30, 2016 and 2015, respectively, and $1.7 million and $3.3 million for the nine months ended September 30, 2016 and 2015, respectively, as a result of removing certain assets from service.