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Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Option Activity

A summary of option activity under the Plans for the years ended December 31, 2020, 2019, and 2018 is as follows:

(in thousands, except for share and per share amounts)			Number of Shares						Weighted Average Exercise Price at Grant Date						Weighted Average Remaining Term (Years)						Aggregate Intrinsic Value
Outstanding at December 31, 2017			4,719,784						$	10.03					5.63						$	24,421
Granted			567,500						19.22
Forfeited			(232,527)						13.99
Exercised			(685,715)						9.12												5,945
Outstanding at December 31, 2018			4,369,042						11.15						5.28						65,438
Granted			687,500						18.38
Forfeited			(53)						7.94
Expired			(15,000)						14.78
Exercised			(546,344)						11.47												2,482
Outstanding at December 31, 2019			4,495,145						12.21						5.58						22,148
Granted			627,500						11.27
Forfeited			(225,000)						18.83
Expired			(557,604)						14.21
Exercised			(733,223)						7.68												2,868
Outstanding at December 31, 2020			3,606,818						12.24						5.76						8,511
Exercisable at December 31, 2020			2,556,394						11.52						4.53						7,302
Vested and expected to vest at December 31, 2020			3,482,804						12.22						5.64						8,337

Summary of RSU Activity

A summary of RSU activity for the Plans for the years ended December 31, 2020, 2019, and 2018 is as follows:

			Number of Shares						Weighted Average Grant Date Fair Value
Unvested at December 31, 2017			1,357,838						$	12.72
Granted			714,086						18.93
Forfeited			(229,603)						15.19
Vested			(528,745)						12.69
Unvested at December 31, 2018			1,313,576						15.68
Granted			937,328						19.46
Forfeited			(75,444)						18.93
Vested			(526,175)						14.54
Unvested at December 31, 2019			1,649,285						18.04
Granted			832,162						11.28
Forfeited			(260,127)						17.35
Vested			(581,757)						16.54
Unvested at December 31, 2020			1,639,563						15.26

Stock-Based Compensation Expense

Stock-based compensation expense recognized for the years ended December 31, 2020, 2019 and 2018 comprised of the following:

			Year Ended December 31,
(in thousands)			2020						2019						2018
Research and development			$	3,804					$	3,207					$	1,290
Selling, general and administrative			9,556						10,251						10,376
Total stock-based compensation expense			$	13,360					$	13,458					$	11,666

Black-Scholes-Merton Option Pricing Model for Employee and Director Stock Options Granted

Assumptions used in the Black-Scholes-Merton option pricing model for employee and director stock options granted during the years ended December 31, 2020, 2019 and 2018 were as follows:

			Year Ended December 31,
			2020						2019						2018
Expected dividend yield			—		%				—		%				—		%
Weighted average expected volatility			51		%				58		%				58		%
Weighted average expected term (years)			6.07						5.95						5.90
Weighted average risk-free rate			1.14		%				2.26		%				2.68		%

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Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement.

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Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year.

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Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.

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