Share-based compensation (Tables)

12 Months Ended

Dec. 31, 2018

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, 2018, 2017 and 2016:

	Year Ended December 31,
(U.S. Dollars, in thousands)	2018		2017		2016
Cost of sales	$	522	$	486	$	553
Sales and marketing		1,802		1,471		1,230
General and administrative		15,197		9,671		13,132
Research and development		1,409		929		1,051
Total	$	18,930	$	12,557	$	15,966

	Year Ended December 31,
(U.S. Dollars, in thousands)	2018		2017		2016
Stock options	$	3,061	$	2,388	$	2,021
Time-based restricted stock awards and stock units		7,265		5,540		6,016
Performance-based restricted stock awards and stock units		1,998		462		5,716
Market-based restricted stock units		5,256		2,904		948
Stock purchase plan		1,350		1,263		1,265
Total	$	18,930	$	12,557	$	15,966

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,
	2018		2017			2016
Assumptions:
Expected term (in years)	4.5		4.5			4.5
Expected volatility	28.7% – 30.1%			31.2	%	30.6% – 32.3%
Risk free interest rate	2.55% – 2.79%			1.93	%	1.07% – 1.92%
Dividend yield	—		—			—
Weighted average grant date fair value	$	16.28	$	13.32		$	11.79

Schedule of Stock Option Plans

Summaries of the status of the Company’s stock option plans as of December 31, 2018 and 2017 and changes during the year ended December 31, 2018 are presented below:

	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at December 31, 2017		1,086,822		$	37.47
Granted		231,548		$	57.66
Exercised		(100,821	)	$	27.80
Forfeited		(41,662	)	$	48.80
Outstanding at December 31, 2018		1,175,887		$	41.87		6.61
Vested and expected to vest at December 31, 2018		1,175,887		$	41.87		6.61
Exercisable at December 31, 2018		696,248		$	36.67		5.36

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, 2018 and 2017 and changes during the year ended December 31, 2018 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, 2017		325,874		$	42.44		109,880		$	33.12		187,314		$	51.99
Granted		172,108		$	57.18		—		$	—		97,420		$	68.38
Vested and settled		(112,249	)	$	40.08		—		$	—		—		$	—
Cancelled		(28,141	)	$	48.84		(7,725	)	$	33.12		(13,439	)	$	60.83
Outstanding at December 31, 2018		357,592		$	49.77		102,155		$	33.12		271,295		$	57.44