Share-based compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Share-Based Compensation by Line Item in Consolidated Statements of Income

The following tables present the detail of share-based compensation by line item in the consolidated statements of income as well as by award type, for the years ended December 31, 2019, 2018, and 2017:

	Year Ended December 31,
(U.S. Dollars, in thousands)	2019		2018		2017
Cost of sales	$	715	$	522	$	486
Sales and marketing		2,512		1,802		1,471
General and administrative		16,872		15,197		9,671
Research and development		1,441		1,409		929
Total	$	21,540	$	18,930	$	12,557

	Year Ended December 31,
(U.S. Dollars, in thousands)	2019		2018		2017
Stock options	$	4,054	$	3,061	$	2,388
Time-based restricted stock awards and stock units		11,084		7,265		5,540
Performance-based restricted stock awards and stock units		—		1,998		462
Market-based restricted stock units		4,733		5,256		2,904
Stock purchase plan		1,669		1,350		1,263
Total	$	21,540	$	18,930	$	12,557

Schedule of Assumptions Used in Determining Fair Value of Stock Options

A summary of the Company’s assumptions used in determining the fair value of the stock options granted during the year is shown in the following table.

	Year Ended December 31,
	2019		2018		2017
Assumptions:
Expected term (in years)	5.0		4.5		4.5
Expected volatility	29.7% – 31.0%		28.7% – 30.1%			31.2	%
Risk free interest rate	1.38% – 2.31%		2.55% – 2.79%			1.93	%
Dividend yield		—	—		—
Weighted average grant date fair value	$	14.64	$	16.28	$	13.32

Schedule of Stock Option Plans

Summaries of the status of the Company’s stock option plans as of December 31, 2019 and 2018 and changes during the year ended December 31, 2019 are presented below:   

	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at December 31, 2018		1,175,887		$	41.87
Granted		279,248		$	49.17
Exercised		(74,729	)	$	37.20
Forfeited or expired		(79,092	)	$	54.84
Outstanding at December 31, 2019		1,301,314		$	42.92		5.69
Vested and expected to vest at December 31, 2019		1,301,314		$	42.92		5.69
Exercisable at December 31, 2019		896,836		$	39.97		4.24

Schedule of Changes in Time-Based, Performance-Based and Market-Based Restricted Stock Awards and Stock Units

A summary of the status of our time-based, performance-based and market-based restricted stock awards and stock units as of December 31, 2019 and 2018 and changes during the year ended December 31, 2019 are presented below:

	Time-based Restricted Stock Awards and Stock Units					Performance-based Restricted Stock Awards and Stock Units					Market-based Restricted Stock Units
	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2018		357,592		$	49.77		102,155		$	33.12		271,295		$	57.44
Granted		319,189		$	52.48		—		$	—		60,722		$	65.27
Vested and settled		(157,053	)	$	46.82		(102,155	)	$	33.12		—		$	—
Cancelled		(51,000	)	$	52.85		—		$	—		(74,855	)	$	15.92
Outstanding at December 31, 2019		468,728		$	51.96		—		$	—		257,162		$	60.08