4. Intangible assets, net

Intangible assets other than goodwill consist of the following:

(In thousands)	Amortization period	March 31, 2017			December 31, 2016
Gross amount:
Software developed for internal use	3-10 years		13,762			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
			109,738			111,264
Accumulated amortization:
Software developed for internal use			(729	)		(505	)
Acquired proprietary technology			(2,986	)		(2,660	)
Customer relationships			(6,037	)		(4,840	)
Trade names			(1,073	)		(916	)
Domain names			(13	)		(10	)
Databases			(4,257	)		(3,354	)
Non-competition agreements			(614	)		(448	)
			(15,709	)		(12,733	)
Net intangible assets:
Software developed for internal use			13,033			10,933
Acquired proprietary technology			8,396			10,872
Customer relationships			28,949			30,146
Trade names			15,284			17,141
Domain names			178			181
Databases			27,035			27,938
Non-competition agreements			1,154			1,320
		$	94,029		$	98,531

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, acquired databases, and non-competition agreements all represent the fair values of intangible assets acquired as a result of the acquisition of Fluent on December 8, 2015 (the “Fluent Acquisition”) and the Q Interactive Acquisition.

During the three months ended March 31, 2017, as a result of the Integration, the remaining balance of intangible assets of $3,560, relating to the acquired proprietary technology and trade names acquired in the Q Interactive Acquisition, was written off into the operating expenses as a write-off of long-lived assets. See Note 3, “Acquisition,” for details.

Amortization expenses of $3,266 and $2,526 were included in depreciation and amortization expenses for the three months ended March 31, 2017 and 2016, respectively. As of March 31, 2017, intangible assets of $6,347, included in the gross amounts of software developed for internal use, have not started amortization. These intangible assets will start to amortize when they are put into use.

As of March 31, 2017, estimated amortization expenses related to the Company’s intangible assets for the remainder of 2017 through 2022 and thereafter are as follows:

(In thousands)
Year	March 31, 2017
Remainder of 2017	$	10,173
2018		13,725
2019		13,447
2020		12,810
2021		9,856
2022 and thereafter		34,018
Total	$	94,029