Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Compensation Cost Related to Share Based Compensation

Share-Based Compensation. The compensation cost that has been included in the statements of operations and comprehensive income (loss) for all share-based compensation arrangements is as follows:

	Year Ended December 31,
(in thousands)	2019		2018		2017
Sales, general and administrative expense	$	49,489	$	31,847	$	27,951
Research and development expense		25,773		26,221		14,571
Share-based compensation expense	$	75,262	$	58,068	$	42,522

Weighted-Average Assumptions for Stock Option Grants using Black-Scholes Option-Pricing Model

The estimated fair value of each stock option award granted was determined on the date of grant using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for option grants:

	Year Ended December 31,
(in thousands)	2019	2018	2017
Risk-free interest rate	2.4%	2.5%	2.0%
Expected volatility of common stock	54.8%	59.5%	58.0%
Dividend yield	0.0%	0.0%	0.0%
Expected option term	5.4 years	4.7 years	5.7 years

Summary and Changes in Stock Options Outstanding

A summary of activity related to stock options follows:

	Year Ended December 31,
	2019					2018					2017
(in thousands, except weighted average data)	Options			Weighted Average Exercise Price		Options			Weighted Average Exercise Price		Options			Weighted Average Exercise Price
Outstanding at January 1		5,746		$	41.38		6,356		$	28.83		6,112		$	20.01
Granted		1,416			82.27		1,040			84.97		1,807			46.55
Exercised		(983	)		27.95		(1,592	)		18.95		(1,353	)		10.41
Canceled		(72	)		75.09		(58	)		64.67		(210	)		43.05
Outstanding at December 31		6,107		$	52.62		5,746		$	41.38		6,356		$	28.83

Summary and Changes in Restricted Stock Units Outstanding

A summary of activity related to RSUs follows:

	Year Ended December 31,
	2019					2018					2017
(in thousands, except weighted average data)	Number of Units			Weighted Average Grant Date Fair Value per Unit		Number of Units			Weighted Average Grant Date Fair Value per Unit		Number of Units			Weighted Average Grant Date Fair Value per Unit
Outstanding at January 1		1,133		$	62.31		1,080		$	40.30		883		$	29.33
Granted		707			82.66		540			85.29		588			47.21
Cancelled		(56	)		74.49		(58	)		36.21		(41	)		40.62
Converted into common shares		(416	)		54.30		(429	)		59.23		(350	)		24.19
Outstanding at December 31		1,368		$	74.77		1,133		$	62.31		1,080		$	40.30