5. Intangible Assets

The following table summarizes the gross carrying amount and accumulated amortization for intangible assets resulting from acquisitions (in thousands):

	Existing			Customer
	Technology			Relationship			Total
Amortization period (in years)		11.75		4.0 – 11.75

Gross carrying amount at December 31, 2016	$	4,600		$	10,639		$	15,239
Accumulated amortization		(2,809	)		(6,610	)		(9,419	)

Intangible Assets, net at December 31, 2016	$	1,791		$	4,029		$	5,820

Gross carrying amount at June 30, 2017	$	4,600		$	10,639		$	15,239
Accumulated amortization		(3,033	)		(7,114	)		(10,147	)

Intangible Assets, net at June 30, 2017	$	1,567		$	3,525		$	5,092

Each period, the Company evaluates the estimated remaining useful lives of purchased intangible assets and whether events or changes in circumstances warrant a revision to the remaining period of amortization. If a revision to the remaining period of amortization is warranted, amortization is prospectively adjusted over the remaining useful life of the intangible asset. Intangible assets subject to amortization are amortized over their useful lives as shown in the table above. The Company evaluates its amortizable intangible assets for impairment at the end of each reporting period. The Company did not identify any impairment indicators during the three and six months ended June 30, 2017.

The following table illustrates the amortization expense included in the condensed consolidated statements of operations for the three and six months ended June 30, 2017 and 2016, respectively (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
Cost of revenue	$	112	$	112	$	224	$	224
Selling and marketing		252		252		504		504
Total	$	364	$	364	$	728	$	728

The estimated annual future amortization expense for purchased intangible assets with definite lives over the next five years as of June 30, 2017 is as follows (in thousands):

2017 (remaining six months)	$	727
2018		1,455
2019		1,455
2020		1,455
Thereafter		—
Total	$	5,092