Intangible Assets, Net

12 Months Ended

Dec. 31, 2016

7.INTANGIBLE ASSETS, NET

The following table provides the gross and net carrying amounts for each major class of intangible assets:



	As of December 31, 2016						As of December 31, 2015
	Gross carrying		Accumulated		Net book		Gross carrying		Accumulated		Net book
	amount		amortization		value		amount		amortization		value

	(in thousands)
Current contract intangibles	$	4,141,968	$	(1,401,025)	$	2,740,943	$	3,904,864	$	(1,118,493)	$	2,786,371
Network location intangibles		1,515,348		(599,367)		915,981		1,446,293		(497,251)		949,042
Intangible assets, net	$	5,657,316	$	(2,000,392)	$	3,656,924	$	5,351,157	$	(1,615,744)	$	3,735,413

All intangible assets noted above are included in the Company’s site leasing segment. The Company amortizes its intangible assets using the straight-line method over 15 years. Amortization expense relating to the intangible assets above was $369.9 million, $363.1 million, and $338.4 million for the years ended December 31, 2016, 2015 and 2014, respectively.

Estimated amortization expense on the Company’s intangibles assets is as follows:



For the year ended December 31,	(in thousands)

2017	$	376,482
2018		376,393
2019		376,095
2020		375,253
2021		342,972