5. Intangible assets, net

Intangible assets other than goodwill consist of the following:

(In thousands)	Amortization period	June 30, 2016			December 31, 2015
Gross amount:
Purchased IP and capitalized litigation costs	10 years	$	3,837		$	1,659
Software developed for internal use	3-10 years		6,795			2,571
Acquired proprietary technology	5 years		13,532			10,716
Customer relationships	7-10 years		34,986			30,875
Trade names	20 years		18,057			16,357
Domain names	20 years		191			191
Acquired databases	5-10 years		31,292			25,052
Non-competition agreements	2-5 years		1,768			728
			110,458			88,149
Accumulated amortization:
Purchased IP and capitalized litigation costs			(48	)		(34	)
Software developed for internal use			(166	)		(50	)
Acquired proprietary technology			(1,307	)		(133	)
Customer relationships			(2,445	)		(272	)
Trade names			(460	)		(50	)
Domain names			(5	)		(1	)
Acquired databases			(1,551	)		(155	)
Non-competition agreements			(115	)		(9	)
			(6,097	)		(704	)
Net intangible assets:
Purchased IP and capitalized litigation costs			3,789			1,625
Software developed for internal use			6,629			2,521
Acquired proprietary technology			12,225			10,583
Customer relationships			32,541			30,603
Trade names			17,597			16,307
Domain names			186			190
Acquired databases			29,741			24,897
Non-competition agreements			1,653			719
		$	104,361		$	87,445

The amount associated with Purchased IP and capitalized litigation costs is mainly related to the intellectual property we purchased from Ole Poulsen (“Purchased IP”) pursuant to the Intellectual Property Purchase Agreement dated October 14, 2014 and related legal and other costs incurred in defending the Company’s claims to the Purchased IP. The gross amount associated with software developed for internal use mainly represent capitalized costs of internally developed software. The amounts relating to acquired proprietary technology, customer relationships, trade names, domain names, acquired databases, and non-competition agreements all represent the fair values of intangible assets acquired as a result of the Fluent Acquisition and Q Interactive Acquisition.

Amortization expenses of $2,867 and $16 were included in depreciation and amortization expenses for the three months ended June 30, 2016 and 2015, respectively, and $5,393 and $28 for the six months ended June 30, 2016 and 2015, respectively. As of June 30, 2016, there were intangible assets of $3,562 and $1,502, included into the gross amounts of Purchased IP and capitalized litigation costs, and software developed for internal use, respectively, that have not started amortization. These intangible assets will start to amortize when they are put into use.

As of June 30, 2016, estimated amortization expenses related to the Company’s intangible assets for the remainder of 2016 through 2021 and thereafter are as follows:

(In thousands)
Year	June 30, 2016
Remainder of 2016	$	6,838
2017		13,876
2018		13,583
2019		13,253
2020		13,018
2021 and thereafter		43,793
	$	104,361