4. Intangible assets, net

Intangible assets other than goodwill consist of the following:

(In thousands)	Amortization period	June 30, 2017			December 31, 2016
Gross amount:
Software developed for internal use	3-10 years		15,850			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
			111,826			111,264
Accumulated amortization:
Software developed for internal use			(991	)		(505	)
Acquired proprietary technology			(3,555	)		(2,660	)
Customer relationships			(7,234	)		(4,840	)
Trade names			(1,277	)		(916	)
Domain names			(15	)		(10	)
Databases			(5,159	)		(3,354	)
Non-competition agreements			(781	)		(448	)
			(19,012	)		(12,733	)
Net intangible assets:
Software developed for internal use			14,859			10,933
Acquired proprietary technology			7,827			10,872
Customer relationships			27,752			30,146
Trade names			15,080			17,141
Domain names			176			181
Databases			26,133			27,938
Non-competition agreements			987			1,320
		$	92,814		$	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, 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 first quarter of 2017, as a result of the Q Interactive 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 to operating expenses as a write-off of long-lived assets. See Note 3, “Acquisition,” for details.

Amortization expenses of $3,303 and $2,867 for the three months ended June 30, 2017 and 2016, respectively, and $6,569 and $5,393 for the six months ended June 30, 2017 and 2016, respectively, were included in depreciation and amortization expenses. As of June 30, 2017, intangible assets of $8,336, included in the gross amounts of software developed for internal use, have not been amortized. These intangible assets will start to amortize when they are put into use.

As of June 30, 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	June 30, 2017
Remainder of 2017	$	6,881
2018		14,009
2019		13,741
2020		13,105
2021		10,032
2022 and thereafter		35,046
Total	$	92,814