Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities Recorded at Fair Value on Recurring Basis

The fair value of the Company’s financial assets and liabilities on a recurring basis were as follows:

(U.S. Dollars in thousands)	Balance December 31, 2014			Level 1		Level 2			Level 3
Assets
Collective trust funds	$	1,696		$	—	$	1,696		$	—
Treasury securities		586			586		—			—
Certificates of deposit		1,510			1,510		—			—
Derivative securities		2,825			—		2,825			—
Total	$	6,617		$	2,096	$	4,521		$	—
Liabilities
Deferred compensation plan	$	(1,886	)	$	—	$	(1,886	)	$	—
Total	$	(1,886	)	$	—	$	(1,886	)	$	—

(U.S. Dollars in thousands)	Balance December 31, 2013			Level 1		Level 2			Level 3
Assets
Collective trust funds	$	1,667		$	—	$	1,667		$	—
Treasury securities		660		660			—			—
Certificates of deposit		1,562			1,562		—			—
Derivative securities		107			—		107			—
Total	$	3,996		$	2,222	$	1,774		$	—
Liabilities
Deferred compensation plan	$	(2,506	)	$	—	$	(2,506	)	$	—
Derivative securities		(1,036	)		—		(1,036	)		—
Total	$	(3,542	)	$	—	$	(3,542	)	$	—