Identifiable intangible assets consist of acquired customer contracts and relationships, trademarks and non-compete agreements. Amortization expense related to intangible assets was $13.9 and $13.5 for the three months ended December 31, 2020 and 2019, respectively. These assets are amortized over their estimated useful lives of which the reasonableness is continually evaluated by the Company.

Intangible assets as of December 31, 2020 and September 30, 2020 consisted of the following:

		December 31, 2020					September 30, 2020
	Estimated Useful Life	Gross Carrying Amount		Accumulated Amortization			Gross Carrying Amount		Accumulated Amortization
Customer relationships	6-21 yrs.	$	682.8	$	(462.0	)	$	666.3	$	(448.3	)
Trademarks	4-12 yrs.		3.8		(2.1	)		3.8		(2.0	)
Non-compete agreements	5 yrs.		2.7		(1.3	)		2.7		(1.2	)
Total intangible assets		$	689.3	$	(465.4	)	$	672.8	$	(451.5	)

The following is a summary of the goodwill activity for the periods ended September 30, 2020 and December 31, 2020:

	Maintenance Services		Development Services			Total
Balance, September 30, 2019	$	1,616.0	$	194.4		$	1,810.4
Acquisitions		64.4		—			64.4
Impairment Loss		—		(15.5	)		(15.5	)
Balance, September 30, 2020		1,680.4		178.9			1,859.3
Acquisitions		39.8		1.2			41.0
Balance, December 31, 2020	$	1,720.2	$	180.1		$	1,900.3

As a result of the 2020 annual goodwill impairment assessment and in conjunction with the initiation and conclusion of the sale of the BrightView Tree Company in the fourth quarter of fiscal 2020, the Company recognized an impairment loss of $15.5. The goodwill impairment loss was recognized during the fourth quarter of fiscal 2020 and was included in Selling, general and administrative expense.

During the three months ended December 31, 2020, the Company acquired, through a series of separate transactions, 100% of the operations of three unrelated companies, one of which was allocated between Maintenance Services and Development Services. The Company paid approximately $62.2 in aggregate 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 customer relationship intangible assets of $16.5. 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.