6. Deferred Legal Fees and Intangible Assets

Deferred legal fees have been incurred in connection with patent litigation for Oxtellar XR and Trokendi XR. As of December 31, 2016 and 2015, the Company had deferred legal fees of $19.9 million and $22.5 million, respectively.

The following sets forth the gross carrying amount and related accumulated amortization of these intangible assets, in thousands:

	Weighted-Average Life	December 31, 2016			December 31, 2015
Capitalized patent defense costs	9.5 - 11 years	$	17,773		$	994
Less accumulated amortization			(1,283	)		(18	)

		$	16,490		$	976

The Company prevailed in a lawsuit related to Oxtellar XR in 2016, at which time the Company reduced deferred legal fees, by $16.6 million, and transferred these amounts to intangible assets. The Company subsequently began amortizing the costs associated with that litigation.

The net book value of intangible assets was $16.5 million as of December 31, 2016 and was $1.0 million as of December 31, 2015. The increase in intangible assets reflects the successful outcome of the lawsuit related to Oxtellar XR in February 2016. There is an offsetting reduction in the amount carried as deferred legal fees, as described above.

Amortization expense on intangible assets was approximately $1.3 million, $0.2 million, and $0.2 million for the years ended December 31, 2016, 2015 and 2014, respectively. Amortization expense in 2015 and 2014 included amortization expense associated with purchased patents that were fully amortized as of December 31, 2015 and are therefore not included in the above table.

There were no indicators of impairment identified at December 31, 2016 or December 31, 2015.