4. GOODWILL AND INTANGIBLE ASSETS-NET

Goodwill consists of the excess of the purchase price over the fair value of identifiable net assets of businesses acquired. The following is the summary of the changes to the carrying amount of goodwill for the three months ended March 31, 2019 and the year ended December 31, 2018:

Of the total goodwill, approximately $90,000 is allocated to the Practice Management segment and the balance is allocated to the Healthcare IT segment.

Intangible assets include customer contracts and relationships and covenants not-to-compete acquired in connection with acquisitions, as well as trademarks acquired and software costs. Intangible assets - net as of March 31, 2019 and December 31, 2018 consist of the following:

Amortization expense was approximately $549,000 and $440,000 for the three months ended March 31, 2019 and 2018, respectively. The weighted-average amortization period is eight years.

As of March 31, 2019, future amortization scheduled to be expensed is as follows: