Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2012

Accounting Policies [Abstract]

Schedule of Useful Lives

The useful lives are as follows:

	Years
Buildings	25 to 33
Plant, equipment and instrumentation	2 to 10
Furniture and fixtures	4 to 8

Components of Changes in Accumulated Other Comprehensive Income

The components of and changes in accumulated other comprehensive income are as follows:

(U.S. Dollars, in thousands)	Foreign Currency Translation Adjustments			Fair Value of Cross- Currency Swaps			Accumulated Other Comprehensive Income (Loss)
Balance at December 31, 2010 (Restated)	$	6,125		$	305		$	6,430
Unrealized loss on cross-currency swaps, net of tax benefit of $256		—			(437	)		(437	)
Foreign currency translation adjustment (1)		(2,279	)		—			(2,279	)
Balance at December 31, 2011 (Restated)		3,846			(132	)		3,714
Unrealized gain on cross-currency swaps, net of tax of $153		—			263			263
Foreign currency translation adjustment (1)		768			—			768
Balance at December 31, 2012 (Restated)	$	4,614		$	131		$	4,745

(1) As the cash generally remains permanently invested in the non U.S. dollar denominated foreign subsidiaries, no deferred taxes are recognized on the related foreign currency translation adjustment.