INTANGIBLE ASSETS AND GOODWILL

The Company's intangible assets at December 31, 2018 and 2017 consisted of the following (in thousands):



December 31, 2018	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600
Developed technology	6.91	182,880		63,187		119,693
Customer relationships	9.44	146,940		22,218		124,722
Trade names	5.20	2,000		624		1,376
Internal use software	3.00	730		730		—
	7.88	$	338,150	$	86,759	$	251,391



December 31, 2017	Weighted average amortization period (years)	Cost		Accumulated amortization		Net carrying value
In-process research and development	*	$	5,600	$	—	$	5,600
Developed technology	6.90	153,380		24,211		129,169
Customer relationships	9.32	120,840		12,015		108,825
Trade names	3.00	900		80		820
Internal use software	3.00	730		730		—
	7.77	$	281,450	$	37,036	$	244,414

* An in-process research and development intangible asset has an indefinite life until the product is generally available, at which time such asset is typically reclassified to developed technology.

Amortization expense for intangible assets for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands):



	Year ended December 31,						Statement of operations classification
	2018		2017		2016		Statement of operations classification
Developed technology	$	38,976	$	18,358	$	6,038	Cost of revenue - product
Customer relationships	10,203		4,145		1,462		Sales and marketing
Trade names	544		80		—		Sales and marketing
	$	49,723	$	22,583	$	7,500

In connection with the preparation of its financial statements for the fourth quarter of 2017, the Company reviewed its intangible assets and other long-lived assets for impairment indicators. The Company determined that a triggering event had occurred relative to one of its developed technology intangible assets that had been previously acquired. During 2017, the Company discontinued its ongoing development of this technology and determined that there were no alternative uses of the technology within either its existing or future product lines. As a result, the Company recorded an impairment charge of $5.5 million to write down the carrying value of the asset to zero. This expense is included as a component of Cost of revenue - product in the table above and in the Company's consolidated statements of operations for the year ended December 31, 2017.

Estimated future amortization expense for the Company's intangible assets at December 31, 2018 was as follows (in thousands):



Years ending December 31,
2019	$	47,411
2020	46,552
2021	40,571
2022	34,156
2023	26,756
Thereafter	55,945
	$	251,391

Goodwill is recorded when the consideration for an acquisition exceeds the fair value of net tangible and identifiable intangible assets acquired. The changes in the carrying value of the Company's goodwill in the years ended December 31, 2018 and 2017 were as follows (in thousands):



	Year ended December 31,
	2018			2017
Balance at January 1
Goodwill	$	338,822		$	52,499
Accumulated impairment losses	(3,106		)	(3,106		)
	335,716			49,393
Acquisition of Edgewater	48,053			—
Acquisition of GENBAND	—			285,825
Acquisition of Taqua and subsequent purchase accounting adjustments	—			498
Write-off of goodwill attributable to dissolved subsidiary	(114		)	—
Balance at December 31	$	383,655		$	335,716