4. Intangible assets, net

Intangible assets other than goodwill consist of the following:

(In thousands)	Amortization period	March 31, 2018			December 31, 2017
Gross amount:
Software developed for internal use	3 years	$	3,308		$	2,972
Acquired proprietary technology	5 years		11,382			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			99,284			98,948
Accumulated amortization:
Software developed for internal use			(655	)		(490	)
Acquired proprietary technology			(5,263	)		(4,693	)
Customer relationships			(10,825	)		(9,628	)
Trade names			(1,891	)		(1,686	)
Domain names			(22	)		(20	)
Databases			(7,866	)		(6,964	)
Non-competition agreements			(1,280	)		(1,113	)
Total accumulated amortization			(27,802	)		(24,594	)
Net intangible assets:
Software developed for internal use			2,653			2,482
Acquired proprietary technology			6,119			6,689
Customer relationships			24,161			25,358
Trade names			14,466			14,671
Domain names			169			171
Databases			23,426			24,328
Non-competition agreements			488			655
Total net intangible assets		$	71,482		$	74,354

The gross amount associated with software developed for internal use mainly represents capitalized costs of internally developed software. The amounts relating to acquired proprietary technology, customer relationships, trade names, domain names, databases and non-competition agreements mainly 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 three months ended March 31, 2017.

Amortization expenses of $3,208 and $3,111 for the three months ended March 31, 2018 and 2017, respectively, were included in depreciation and amortization expenses. As of March 31, 2018, intangible assets with the carrying amount of $1,317, included in the gross amounts of software developed for internal use, have not started amortization as they are not ready for their intended use.

As of March 31, 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	March 31, 2018
Remainder of 2018	$	9,561
2019		12,751
2020		12,107
2021		8,892
2022		7,999
2023 and thereafter		20,172
Total	$	71,482