Revenue recognition and accounts receivable (Tables)

12 Months Ended

Dec. 31, 2017

Revenue Recognition And Accounts Receivable [Abstract]

Schedule of Net Sales

The table below presents net sales, which includes product sales and marketing service fees, for each of the years ended December 31, 2017, 2016, and 2015.

	For the year ended December 31,
(U.S. Dollars, in thousands)	2017		2016		2015
Product sales	$	373,538	$	355,652	$	341,084
Marketing service fees		60,285		54,136		55,405
Net sales	$	433,823	$	409,788	$	396,489