Intangible assets as of September 30, 2018 and September 30, 2017 consist of the following:

		September 30, 2018					September 30, 2017
	Useful Life	Gross Carrying Amount		Accumulated Amortization			Gross Carrying Amount		Accumulated Amortization
Customer relationships	6-21 yrs.	$	622,710	$	(337,800	)	$	600,515	$	(275,993	)
Trademarks	4-12 yrs.		230,900		(227,520	)		230,900		(184,151	)
Non-compete agreements	5 yrs.		2,320		(155	)		—		—
Total intangible assets		$	855,930	$	(565,475	)	$	831,415	$	(460,144	)

Amortization expense related to intangible assets was $104,943, $92,863 and $131,562 for the year ended September 30, 2018, the nine months ended September 30, 2017 and the year ended December 31, 2016, respectively.

The following table shows changes in the carrying amount of goodwill from January 1, 2017 to September 30, 2018 by reportable segment:

	Maintenance Services		Development Services		Total
Balance, January 1, 2017	$	1,486,640	$	180,474	$	1,667,114
Acquisitions		36,659		—		36,659
Balance, September 30, 2017		1,523,299		180,474		1,703,773
Acquisitions		49,064		13,924		62,988
Balance, September 30, 2018	$	1,572,363	$	194,398	$	1,766,761

The weighted average amortization period for intangible assets is 14.7 years. Amortization expense is anticipated to be as follows in future years:

Year Ended September 30,
2019	$	55,580
2020		47,551
2021		39,723
2022		32,691
2023		26,505
2024 and thereafter		87,405
	$	289,455

During the year ended September 30, 2018, the Company acquired, through a series of separate transactions, 100% of the operations of five unrelated Maintenance Services companies. The Company paid approximately $104,377 in consideration for the acquisitions, net of cash acquired. The Company accounted for the business combinations under the acquisition method and, accordingly, recorded the assets acquired and liabilities assumed at their estimated fair market values based on management’s preliminary estimates, with the excess allocated to goodwill. The fair values were primarily estimated using Level 3 assumptions within the fair value hierarchy, including estimated future cash flows, discount rates and other factors. The valuation process to determine fair values is not yet complete. The Company will finalize the amounts recognized as it obtains the information necessary to complete the analysis, but no later than one year from the acquisition date. The identifiable assets acquired were primarily intangible assets, including customer relationships and non-compete agreements of $24,515. The amount allocated to goodwill is reflective of the benefits the Company expects to realize from anticipated synergies and the acquired assembled workforce. The Company expects a portion of the goodwill resulting from these acquisitions will be deductible for tax purposes.