8. Intangible assets, net

Intangible assets other than goodwill consist of the following:

(In thousands)	Amortization period	December 31, 2017			December 31, 2016
Gross amount:
Software developed for internal use	3-10 years		19,614			11,438
Acquired proprietary technology	5 years		11,382			13,532
Customer relationships	7-10 years		34,986			34,986
Trade names	20 years		16,357			18,057
Domain names	20 years		191			191
Databases	5-10 years		31,292			31,292
Non-competition agreements	2-5 years		1,768			1,768
			115,590			111,264
Accumulated amortization:
Software developed for internal use			(1,779	)		(505	)
Acquired proprietary technology			(4,693	)		(2,660	)
Customer relationships			(9,628	)		(4,840	)
Trade names			(1,686	)		(916	)
Domain names			(20	)		(10	)
Databases			(6,964	)		(3,354	)
Non-competition agreements			(1,113	)		(448	)
			(25,883	)		(12,733	)
Net intangible assets:
Software developed for internal use			17,835			10,933
Acquired proprietary technology			6,689			10,872
Customer relationships			25,358			30,146
Trade names			14,671			17,141
Domain names			171			181
Databases			24,328			27,938
Non-competition agreements			655			1,320
		$	89,707		$	98,531

The Company recorded the intellectual property purchased by the Company’s subsidiary, TBO, from Ole Poulsen (“Purchased IP”), pursuant to the Intellectual Property Purchase Agreement dated October 14, 2014, and related legal and other costs incurred and paid in defending the Company’s claims to the Purchased IP against TransUnion Risk and Alternative Data Solutions, Inc. (“TRADS”), in intangible assets as Purchased IP and capitalized litigation costs. In 2016, the Company wrote off the remaining balance of Purchased IP and capitalized litigation costs of $4,055, which is reflected in costs and expenses as write-off of long-lived assets in the consolidated statements of operations for the year ended December 31, 2016, as a result of an unfavorable ruling in relation to the litigation.

As a result of the Q Interactive Integration approved on January 18, 2017, 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.

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 all represent the fair values of intangible assets acquired as a result of the Fluent Acquisition and the Q Interactive Acquisition.

Amortization expenses of $13,440, $12,084 and $698 were included in depreciation and amortization expenses for the years ended December 31, 2017, 2016 and 2015, respectively. As of December 31, 2017, intangible assets of $3,869, included in the gross amounts of software developed for internal use, have not started amortization, as they are not ready for their intended use.

The Company capitalized $8,176 and $11,318 during the years ended December 31, 2017 and 2016, with $8,176 and $8,867 related to internally developed software, and $0 and $2,451 related to purchased intellectual property litigation costs, respectively.

As of December 31, 2017, estimated amortization expenses related to the Company’s intangible assets for 2018 through 2023 and thereafter are as follows:

(In thousands)
Year	December 31, 2017
2018	$	14,236
2019		14,307
2020		13,664
2021		10,500
2022		9,661
2023 and thereafter		27,339
Total	$	89,707