Intangible assets, net

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



(In thousands)	Amortization period	March 31, 2019			December 31, 2018
Gross amount:
Software developed for internal use	3 years	$	3,125		$	3,037
Acquired proprietary technology	5 years	11,459			11,459
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		99,178			99,090
Accumulated amortization:
Software developed for internal use		(1,210		)	(1,282		)
Acquired proprietary technology		(7,558		)	(6,987		)
Customer relationships		(15,613		)	(14,417		)
Trade names		(2,709		)	(2,504		)
Domain names		(32		)	(29		)
Databases		(11,475		)	(10,573		)
Non-competition agreements		(1,522		)	(1,486		)
Total accumulated amortization		(40,119		)	(37,278		)
Net intangible assets:
Software developed for internal use		1,915			1,755
Acquired proprietary technology		3,901			4,472
Customer relationships		19,373			20,569
Trade names		13,648			13,853
Domain names		159			162
Databases		19,817			20,719
Non-competition agreements		246			282
Total net intangible assets		$	59,059		$	61,812

The gross amounts associated with software developed for internal use primarily represent capitalized costs for 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, effective on June 8, 2016 (the "Q Interactive Acquisition").

For the three months ended March 31, 2019 and 2018, amortization expense related to intangible assets and included in depreciation and amortization expense in the Company's condensed consolidated statements of operations was $3,125 and $3,208, respectively. As of March 31, 2019, intangible assets with a carrying amount of $607, included in the gross amount of software developed for internal use, have not commenced amortization, as they are not ready for their intended use.

As of March 31, 2019, estimated amortization expenses related to the Company's intangible assets for the remainder of 2019 through 2024 and thereafter are as follows:



(In thousands)
Year	March 31, 2019
Remainder of 2019	$	9,525
2020	12,427
2021	8,886
2022	8,049
2023	3,967
2024 and thereafter	16,205
Total	$	59,059