Intangible assets, net

Intangible assets, other than goodwill, consist of the following:



(In thousands)	Amortization period	September 30, 2018			December 31, 2017
Gross amount:
Software developed for internal use	3 years	$	4,254		$	2,972
Acquired proprietary technology	5 years	11,459			11,382
Customer relationships	7-10 years	34,986			34,986
Trade names	20 years	16,357			16,357
Domain names	20 years	191			191
Databases	5-10 years	31,292			31,292
Non-competition agreements	2-5 years	1,768			1,768
Total gross amount		100,307			98,948
Accumulated amortization:
Software developed for internal use		(1,001		)	(490		)
Acquired proprietary technology		(6,411		)	(4,693		)
Customer relationships		(13,220		)	(9,628		)
Trade names		(2,300		)	(1,686		)
Domain names		(27		)	(20		)
Databases		(9,670		)	(6,964		)
Non-competition agreements		(1,613		)	(1,113		)
Total accumulated amortization		(34,242		)	(24,594		)
Net intangible assets:
Software developed for internal use		3,253			2,482
Acquired proprietary technology		5,048			6,689
Customer relationships		21,766			25,358
Trade names		14,057			14,671
Domain names		164			171
Databases		21,622			24,328
Non-competition agreements		155			655
Total net intangible assets		$	66,065		$	74,354

The gross amounts associated with software developed for internal use primarily represent capitalized costs of internally developed software. The amounts relating to acquired proprietary technology, customer relationships, trade names, domain names, databases and non-competition agreements primarily represent the fair values of intangible assets acquired as a result of the acquisition of Fluent, LLC ("Fluent LLC") effective on December 8, 2015 (the "Fluent LLC Acquisition") and the acquisition of Q Interactive, LLC ("Q Interactive") effective on June 8, 2016 (the "Q Interactive Acquisition").

On January 18, 2017, the Company's management and Board of Directors approved a plan to merge and fully integrate Q Interactive's business into Fluent LLC (the "Q Interactive Integration"). As a result, the remaining balance of long-lived assets of $3,626, relating primarily to the acquired proprietary technology and trade names acquired in the Q Interactive Acquisition, was written off to costs and expenses as a write-off of long-lived assets during the first quarter of 2017.

Amortization expense of $3,228 and $3,146 for the three months ended and $9,653 and $9,404 for the nine months ended September 30, 2018 and 2017, respectively, were included in depreciation and amortization expenses. As of September 30, 2018, intangible assets with the carrying amount of $2,101, included in the gross amount of software developed for internal use, have not started amortization, as they are not ready for their intended use.

As of September 30, 2018, estimated amortization expenses related to the Company's intangible assets for the remainder of 2018 through 2023 and thereafter are as follows:



(In thousands)
Year	September 30, 2018
Remainder of 2018	$	3,271
2019	13,083
2020	12,331
2021	9,190
2022	8,009
2023 and thereafter	20,181
Total	$	66,065