Share-based compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

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

The following tables present the detail of share-based compensation by line item in the consolidated statements of operations as well as by award type, for the years ended December 31, 2017, 2016 and 2015:

	Year Ended December 31,
(U.S. Dollars, in thousands)	2017		2016		2015
Cost of sales	$	486	$	553	$	440
Sales and marketing		1,471		1,230		1,304
General and administrative		9,671		13,132		5,051
Research and development		929		1,051		419
Total	$	12,557	$	15,966	$	7,214

	Year Ended December 31,
(U.S. Dollars, in thousands)	2017		2016		2015
Stock options	$	2,388	$	2,021	$	1,437
Time-based restricted stock awards		5,540		6,016		4,606
Performance-based restricted stock awards		462		5,716	—
Performance-based and market-based restricted stock units		2,904		948		—
Stock purchase plan		1,263		1,265		1,171
Total	$	12,557	$	15,966	$	7,214

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,
Assumptions:	2017			2016		2015
Expected term (in years)	4.5			4.5		4.5
Expected volatility		31.2	%	30.6% – 32.3%		31.1% – 31.6%
Risk free interest rate		1.93	%	1.07% – 1.92%		1.37% – 1.54%
Dividend yield	—			—		—
Weighted average grant date fair value	$	13.32		$	11.79	$	9.49

Schedule of Stock Option Plans

Summaries of the status of the Company’s stock option plans as of December 31, 2017 and 2016 and changes during the year ended December 31, 2017 are presented below:

	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at December 31, 2016		1,137,179		$	36.05
Granted		165,595		$	46.10
Exercised		(152,027	)	$	34.14
Forfeited		(63,925	)	$	42.50
Outstanding at December 31, 2017		1,086,822		$	37.47		7.06
Vested and expected to vest at December 31, 2017		1,086,822		$	37.47		7.06
Exercisable at December 31, 2017		608,320		$	34.33		5.94

Schedule of Stock Options Outstanding and Exercisable by Exercise Price Range

The table below summarizes the options outstanding and exercisable by exercise price range as of December 31, 2017:

	Options Outstanding						Options Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life		Weighted Average Exercise Price		Number Exercisable		Weighted Average Exercise Price
$21.78 – $27.97		111,874		5.08	$	24.12		111,874	$	24.12
$27.98 – $32.28		110,400		5.36	$	31.12		91,326	$	30.90
$33.12 – $33.12		140,475		7.50	$	33.12		70,242	$	33.12
$33.24 – $36.25		121,875		6.74	$	35.51		83,213	$	35.71
$36.46 – $38.40		39,750		8.55	$	37.92		12,376	$	37.64
$38.82 – $38.82		150,000		5.20	$	38.82		150,000	$	38.82
$39.66 – $41.37		65,500		6.12	$	40.23		43,000	$	40.25
$42.89 – $42.89		22,000		8.74	$	42.89		5,500	$	42.89
$44.39 – $44.39		163,138		8.50	$	44.39		40,789	$	44.39
$46.10 – $46.10		161,810		9.50	$	46.10		—	$	—
$21.78 – $46.10		1,086,822		7.06	$	37.47		608,320	$	34.33

Schedule of Changes in Restricted Stock and Stock Units

A summary of the status of our restricted stock and stock units as of December 31, 2017 and 2016 and changes during the year ended December 31, 2017 are presented below:

	Time-based Awards and Units					Performance-based Awards					Performance-based or Market-based Stock Units
	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Non-vested as of December 31, 2016		358,919		$	38.27		192,310		$	34.45		151,575		$	43.54
Granted		143,469		$	46.42		—		$	—		94,902		$	54.49
Vested		(157,807	)	$	37.04		(136,980	)	$	34.99		—		$	—
Cancelled		(18,707	)	$	38.59		—		$	—		(4,613	)	$	49.09
Non-vested as of December 31, 2017		325,874		$	42.44		55,330		$	33.12		241,864		$	47.73