The reconciliation of intangible assets for the year ended December 31, 2019 and the six months ended December 31, 2018 was as follows (in thousands):

	Year Ended			Six Months Ended
	December 31,			December 31,
	2019			2018
Patented technologies
Gross carrying amount at beginning of period	$	68,322		$	68,322
Gross carrying amount at end of period		68,322			68,322
Accumulated amortization at beginning of period		(38,193	)		(36,964	)
Amortization expense		(2,460	)		(1,229	)
Accumulated amortization at end of period		(40,653	)		(38,193	)
Net book value at end of period	$	27,669		$	30,129

The net book value of the Company’s intangible assets at December 31, 2019 and 2018 is summarized as follows (in thousands):

					Estimated
					Remaining
					Useful Life at
	December 31,		December 31,		December 31,
	2019		2018		2019
					(Years)
Patented technologies
DEXYCU / Verisome	$	27,669	$	30,129		11.25
	$	27,669	$	30,129

The Company amortizes its intangible assets with finite lives on a straight-line basis over their respective estimated useful lives. Amortization expense totaled $2.5 million in the year ended December 31, 2019, $1.2 million in the six months ended December 31, 2018, $981,000 in fiscal 2018, and $724,000 in fiscal 2017.

In connection with the Icon Acquisition (see Note 3), the initial purchase price of $32.0 million was attributed to the DEXYCU product intangible asset. This finite-lived intangible asset is being amortized on a straight-line basis over its expected remaining useful life of 11.25 years at the rate of approximately $2.5 million per year. Amortization expense was reported as a component of cost of sales for the year ended December 31, 2019 and was included in research and development for the six months ended December 31, 2018, and the fiscals 2018 and 2017.