8. Intangible Assets

Intangible assets as of March 31, 2018 and December 31, 2017 consist of the following:

	Weighted Average Remaining Useful Life		March 31, 2018			December 31, 2017
			(in thousands)
Acquired technology	16 Months		$	7,252		$	7,252
Acquired intellectual property		—	80			80
Accumulated amortization				(1,070	)		(1,020	)
Total			$	6,262		$	6,312

The estimated useful life of acquired technology and intellectual property is two to three years. The Company evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets.

Amortization expense related to intangible assets was $50 thousand in three months ended March 31, 2018, and $16 thousand in three months ended March 31, 2017. Amortization expense of acquired technology is included in cost of subscription revenue in the consolidated statements of operations. Amortization expense of acquired intellectual property is included in sales and marketing expense in the consolidated statements of operations.

Estimated future amortization expense for intangible assets, currently being amortized, as of March 31, 2018 is as follows:

Years ended December 31,	Amortization Expense
	(in thousands)
2018	$	150
2019		112
Total	$	262

The estimated amortization does not include the amortization of the $6.0 million of acquired technology from the acquisition of Motion AI, Inc. as the intangible asset has not been placed into service as of March 31, 2018. The Company expects that the acquired technology will be placed into service during 2018 and will be amortized through 2020.