Fair value measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

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

The Company’s collective trust funds, treasury securities, equity warrants, equity securities, debt security, contingent consideration, and deferred compensation plan liabilities are the only financial instruments recorded at fair value on a recurring basis as follows:

(U.S. Dollars, in thousands)	Balance December 31, 2018			Level 1		Level 2			Level 3
Assets
Treasury securities	$	490		$	490	$	—		$	—
Equity warrants		—			—		—			—
Equity securities		219			—		219			—
Debt security		17,820			—		—			17,820
Total	$	18,529		$	490	$	219		$	17,820
Liabilities
Contingent consideration	$	(28,560	)	$	—	$	—		$	(28,560	)
Deferred compensation plan		(1,275	)		—		(1,275	)		—
Total	$	(29,835	)	$	—	$	(1,275	)	$	(28,560	)

(U.S. Dollars, in thousands)	Balance December 31, 2017			Level 1		Level 2			Level 3
Assets
Collective trust funds	$	100		$	—	$	100		$	—
Treasury securities		556			556		—			—
Debt security		16,050			—		—			16,050
Total	$	16,706		$	556	$	100		$	16,050
Liabilities
Deferred compensation plan	$	(1,379	)	$	—	$	(1,379	)	$	—
Total	$	(1,379	)	$	—	$	(1,379	)	$	—

Schedule of Changes in Valuation of Securities

The changes in valuation of these securities for the years ended December 31, 2018 and 2017 are shown below:

(U.S. Dollars, in thousands)	2018			2017		2016
Equity securities and warrants at January 1	$	2,768		$	2,768	$	2,768
Impact of adoption of ASU 2016-01 recognized in other income		1,629			—		—
Purchase of additional common stock		500			—		—
Fair value adjustments, expirations, and impairments recognized in other expense		(4,678	)		—		—
Equity securities and warrants at December 31	$	219		$	2,768	$	2,768

Schedule of Reconciliation For Contingent Consideration Measured At Fair Value Using Significant Unobservable Inputs

The following table provides a reconciliation of the beginning and ending balances for the contingent consideration measured at fair value using significant unobservable inputs (Level 3):

(U.S. Dollars, in thousands)	2018
Contingent consideration at January 1	$	—
Acquisition date fair value		25,491
Increase in fair value recognized in operating expenses		3,069
Contingent consideration at December 31	$	28,560

Fair Value, Inputs, Level 3 [Member]

Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]

Schedule of Reconciliation of Available for Sale Debt Securities

The following table provides a reconciliation of the beginning and ending balances for debt securities measured at fair value using significant unobservable inputs (Level 3):

(U.S. Dollars, in thousands)	2018		2017
Balance at January 1	$	16,050	$	12,220
Accrued interest income		—		—
Gains (losses) recorded for the period
Recognized in net income		—		(5,585	)
Recognized in other comprehensive income		1,770		9,415
Balance at December 31	$	17,820	$	16,050