CAPITALIZED FEES PAID TO A RELATED PARTY

12 Months Ended

Dec. 31, 2017

CAPITALIZED FEES PAID TO A RELATED PARTY

CAPITALIZED FEES PAID TO A RELATED PARTY

5. CAPITALIZED FEES PAID TO A RELATED PARTY

        Capitalized fees paid to a related party, which consist of registrational and launch-related milestone fees paid to GSK, were as follows:

		December 31,
	Amortization period
(In thousands)		2017			2016
United States	2013 - 2030	$	120,000		$	120,000
Europe	2013 - 2029		60,000			60,000
Japan	2013 - 2029		40,000			40,000
Gross carrying value			220,000			220,000
Accumulated amortization			(53,278	)		(39,455	)
Net carrying value		$	166,722		$	180,545

        These milestone fees are being amortized over their estimated useful lives commencing upon the commercial launch of the product in their respective regions with the amortization expense recorded as a reduction in revenue from collaborative arrangements. As of December 31, 2017, the weighted average remaining amortization period is 12.1 years.

        Additional information regarding these milestone fees is included in Note 3, "Collaborative Arrangements." Amortization expense for the years ended December 31, 2017, 2016 and 2015 was $13.8 million, respectively. The remaining estimated amortization expense is $13.8 million for each of the years from 2018 to 2022 and $97.7 million thereafter.