Other Intangible Assets, net

The following presents a summary of other intangible assets:



		December 31,
		2018							2017
(millions)	Weighted Average Life (Years)	Acquired Intangible Assets, Gross (1)		Accumulated Amortization			Acquired Intangible Assets, Net		Acquired Intangible Assets, Gross (1)		Accumulated Amortization			Acquired Intangible Assets, Net
Covenant not to compete	4.9	$	1.6	$	—		$	1.6	$	0.9	$	(0.9	)	$	—
Trade names and trademarks	4.9	6.3		(0.7		)	5.6		9.8		(9.7		)	0.1
Proprietary know how	5.7	11.0		(0.8		)	10.2		34.6		(34.5		)	0.1
Management contract rights	10.0	81.0		(32.2		)	48.8		81.0		(27.1		)	53.9
Customer relationships	14.9	100.4		(0.6		)	99.8		—		—			—
Acquired intangible assets, net (2)	12.5	$	200.3	$	(34.3	)	$	166.0	$	126.3	$	(72.2	)	$	54.1

(1) Excludes the original cost and accumulated amortization on fully amortized intangible assets.

(2) Intangible assets have estimated remaining lives between a half year and 16 years.

The table below shows the amortization expense related to intangible assets for the years ended December 31, 2018, 2017 and 2016, and is included in Depreciation and amortization within the Consolidated Statements of Income.



	Year Ended December 31,
(millions)	2018		2017		2016
Amortization expense	$	6.1	$	7.2	$	14.6

The expected future amortization of intangible assets as of December 31, 2018 is as follows:



(millions)	Intangible asset amortization
2019	$	15.1
2020	15.1
2021	15.1
2022	15.0
2023	14.9
2024 and thereafter	90.8
Total	$	166.0