Revenue recognition (Tables)

6 Months Ended

Jun. 30, 2017

Revenue Recognition [Abstract]

Schedule of Net Sales

The table below presents net sales, which includes product sales and marketing service fees, for both the three and six months ended June 30, 2017 and 2016.

	Three Months Ended June 30,				Six Months Ended June 30,
(U.S. Dollars, in thousands)	2017		2016		2017		2016
Product sales	$	93,908	$	90,868	$	182,309	$	176,493
Marketing service fees		15,034		13,207		29,371		26,261
Net sales	$	108,942	$	104,075	$	211,680	$	202,754