Derivative instruments (Tables)

12 Months Ended

Dec. 31, 2014

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Schedule of Fair Values of Derivative Instruments

The tables below disclose the types of derivative instruments the Company owns, the classifications and fair values of these instruments within the balance sheet, and the amount of gain (loss) recognized in other comprehensive income (loss) (“OCI”) or net income (loss).

(U.S. Dollars, in thousands)	Fair value:favorable (unfavorable)			Balance sheetlocation
As of December 31, 2014
Cross-currency swap	$	2,504		Other long-term assets
Warrants	$	321		Other long-term assets
As of December 31, 2013
Cross-currency swap	$	(1,036	)	Other long-term liabilities
Warrants	$	107		Other long-term assets

Schedule of Gain (Loss) Recognized on Derivative Instruments

	For the year ended December 31,
(U.S. Dollars in thousands)	2014			2013			2012
Cross-currency swap gain (loss) recorded in other    comprehensive income (loss), net of taxes	$	251		$	(278	)	$	263
Warrants unrealized gain (loss) recorded in other    comprehensive income (loss), net of taxes	$	(3	)	$	(1	)	$	—