Share-based compensation plans (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

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

The following tables show the detail of share-based compensation by line item in the consolidated statements of operations as well as by grant type, for the years ended December 31, 2015, 2014 and 2013 and the assumptions for each of these years in which grants were awarded:

	Year Ended December 31,
(U.S. Dollars in thousands)	2015		2014		2013
Cost of sales	$	440	$	137	$	104
Sales and marketing		1,304		1,701		1,444
General and administrative		5,051		3,578		4,483
Research and development		419		308		236
Total	$	7,214	$	5,724	$	6,267

	Year Ended December 31,
(U.S. Dollars in thousands)	2015		2014		2013
Stock options	$	1,437	$	1,391	$	2,753
Restricted stock awards		4,606		3,400		1,964
Stock purchase plan		1,171		933		1,550
Total	$	7,214	$	5,724	$	6,267

Schedule of Share-based Payment Award, Valuation Assumptions

	Year Ended December 31,
Assumptions:	2015		2014		2013
Expected term	4.50 years		5.00 years		5.00 years
Expected volatility	31.1% – 31.6%		31.7% – 34.5%		32.1% – 50.8%
Risk free interest rate	1.37% – 1.54%		1.52% – 1.70%		0.58% – 1.52%
Dividend rate	—		—		—
Weighted average fair value of options granted during the year	$	9.49	$	10.45	$	10.83

Schedule of Stock Option Activity

Summaries of the status of the Company’s stock option plans as of December 31, 2015 and 2014 and changes during the year ended December 31, 2015 are presented below:

	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
Outstanding at December 31, 2014		1,527,836		$	34.91
Granted		208,890		$	33.28
Exercised		(93,184	)	$	31.19
Forfeited		(230,940	)	$	38.92
Outstanding at December 31, 2015		1,412,602		$	34.26		5.22
Vested and expected to vest at December 31, 2015		1,332,992		$	34.39		5.02
Options exercisable at December 31, 2015		795,350		$	35.06		2.96

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, 2015:

	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
$10.42 – $21.78		131,000		6.23	$	21.07		71,004	$	20.65
$22.75 – $27.98		133,333		5.51	$	25.14		93,333	$	24.86
$28.29 – $31.40		131,500		3.66	$	29.30		114,000	$	29.29
$31.83 – $32.28		98,150		6.96	$	32.11		42,500	$	31.99
$33.12 – $33.12		165,990		9.10	$	33.12		—	$	—
$33.24 – $36.25		148,650		8.26	$	35.64		30,284	$	36.25
$36.46 – $38.11		129,592		1.35	$	37.90		119,842	$	38.02
$38.82 – $39.94		299,687		4.56	$	39.32		149,687	$	39.81
$41.37 – $44.97		156,200		2.32	$	44.10		156,200	$	44.10
$45.84 – $50.99		18,500		0.92	$	48.43		18,500	$	48.43
$10.42 – $50.99		1,412,602		5.22	$	34.26		795,350	$	35.06

Schedule of Changes in Restricted Stock

A summary of the status of our restricted stock as of December 31, 2015 and 2014 and changes during the year ended December 31, 2015 are presented below:

	Service-based Awards					Performance-based Awards
	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Non-vested as of December 31, 2014		374,926		$	30.47		86,050		$	36.25
Granted		203,618		$	33.27		110,660		$	33.12
Vested		(183,216	)	$	30.35		–		$	–
Cancelled		(16,190	)	$	27.42		(4,400	)	$	36.25
Non-vested as of December 31, 2015		379,138		$	32.15		192,310		$	34.45