The components of other intangible assets, net, at June 30, 2021 (unaudited) and December 31, 2020 were as follows:

			June 30, 2021							December 31, 2020
(millions)	Weighted Average Life (Years)		Intangible Assets, Gross		Accumulated Amortization			Intangible Assets, Net		Intangible Assets, Gross		Accumulated Amortization			Intangible Assets, Net
Covenant not to compete		1.8	$	2.9	$	(1.8	)	$	1.1	$	2.9	$	(1.3	)	$	1.6
Trade names and trademarks		2.4		0.9		(0.3	)		0.6		0.9		(0.2	)		0.7
Proprietary know how		3.2		3.8		(0.9	)		2.9		3.8		(0.4	)		3.4
Management contract rights		7.6		81.0		(45.1	)		35.9		81.0		(42.6	)		38.4
Customer relationships		12.4		21.5		(3.2	)		18.3		21.5		(2.5	)		19.0
Other intangible assets, net		8.8	$	110.1	$	(51.3	)	$	58.8	$	110.1	$	(47.0	)	$	63.1

Amortization expense related to intangible assets for the three and six months ended June 30, 2021 and 2020, (unaudited), respectively, which was included in Depreciation and amortization within the Condensed Consolidated Statements of Income (Loss), was as follows:

As discussed in Note 1. Significant Accounting Policies and Practices, due to the impact of COVID-19 on the Company’s expected future operating cash flows, the Company determined certain impairment triggers had occurred for Proprietary know how intangible assets as of June 30, 2020. Accordingly, the Company analyzed undiscounted cash flows for these intangible assets as of June 30, 2020, and determined the carrying value for the Proprietary know how intangible assets was higher than their projected undiscounted cash flows. The fair value of the Proprietary know how intangible assets, which was classified as Level 3 in the fair value hierarchy, was determined based on estimates of future discounted cash flows using the relief from royalty approach. Proprietary know how intangible assets with a carrying amount of $7.6 million were determined to have a fair value of $3.9 million, resulting in an impairment charge of $3.7 million in the Aviation segment during the three and six months ended June 30, 2020, respectively, which was recognized in Impairment of intangible assets in the Condensed Consolidated Statements of Income (Loss).