(7) INTANGIBLE ASSETS

Identifiable acquisition-related intangible assets as of June 30, 2015 and 2014 were as follows (in millions):

	Gross Carrying Amount		Accumulated Amortization			Net
June 30, 2015
Finite-Lived Intangible Assets
Customer relationships	$	1,080.3	$	(155.0	)	$	925.3
Trade names		0.2		(0.1	)		0.1
Underlying rights		1.7		(0.2	)		1.5
Total		1,082.2		(155.3	)		926.9
Indefinite-Lived Intangible Assets
Certifications		3.5		—			3.5
Underlying Rights		17.9		—			17.9
Total	$	1,103.6	$	(155.3	)	$	948.3
June 30, 2014
Finite-Lived Intangible Assets
Customer relationships	$	789.2	$	(103.6	)	$	685.6
Trade names		0.1		—			0.1
Underlying rights		1.8		(0.1	)		1.7
Total		791.1		(103.7	)		687.4
Indefinite-Lived Intangible Assets
Certifications		3.5		—			3.5
Underlying rights		19.4		—			19.4
Total	$	814.0	$	(103.7	)	$	710.3

The weighted average remaining amortization period for the Company’s customer relationships and trade name assets is 16.3 years and 1.0 years, respectively. The Company has determined that certain underlying rights (including easements) and the certifications have indefinite lives. The amortization period for underlying rights (including easements) is 20 years. The amortization of intangible assets for the years ended June 30, 2015, 2014 and 2013 was $54.8 million, $44.0 million, and $44.4 million, respectively.

During the years ended June 30, 2015 and 2014, the Company wrote off $3.5 million and $27.2 million in fully amortized intangible assets, respectively. Estimated future amortization of finite-lived intangible assets is as follows (in millions):

Year Ended June 30,
2016	$	66.3
2017		66.2
2018		66.2
2019		66.2
2020		62.6
Thereafter		599.4
Total	$	926.9