Equity Incentive Plans and Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Schedule of shares available for grant

A summary of shares available for grant under the Company’s plans is as follows:

	Shares Available for Grant
Total shares available for grant as of December 31, 2019	6,826,863
Increase in shares approved for issuance (1)	7,800,000
Stock options granted	(40,000)
Stock options forfeited	101,816
Nonvested equity stock and stock units granted (2) (3)	(3,528,401)
Nonvested equity stock and stock units forfeited (2)	1,252,042
Total shares available for grant as of December 31, 2020	12,412,320
Stock options forfeited	54,327
Nonvested equity stock and stock units granted (2) (4)	(3,918,251)
Nonvested equity stock and stock units forfeited (2)	1,943,782
Total shares available for grant as of December 31, 2021	10,492,178
Nonvested equity stock and stock units granted (2) (5)	(4,107,633)
Nonvested equity stock and stock units forfeited (2)	1,271,224
Total shares available for grant as of December 31, 2022	7,655,769

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(1)    On April 30, 2020, the Company’s stockholders approved an additional 7,800,000 shares for issuance under the 2015 Plan.

(2)    For purposes of determining the number of shares available for grant under the 2015 Plan against the maximum number of shares authorized, each restricted stock granted reduces the number of shares available for grant by 1.5 shares and each restricted stock forfeited increases shares available for grant by 1.5 shares.

(3)    Amount includes approximately 0.5 million shares that have been reserved for potential future issuance related to certain performance unit awards granted in 2020 and discussed under the section titled “Nonvested Equity Stock and Stock Units” below.

(4)    Amount includes approximately 0.4 million shares that have been reserved for potential future issuance related to certain performance unit awards granted in 2021 and discussed under the section titled “Nonvested Equity Stock and Stock Units” below.

(5)    Amount includes approximately 0.6 million shares that have been reserved for potential future issuance related to certain performance unit awards granted in 2022 and discussed under the section titled “Nonvested Equity Stock and Stock Units” below.

Schedule of stock option activity

The following table summarizes stock option activity under the Company’s equity incentive plans for the years ended December 31, 2022, 2021 and 2020 and information regarding stock options outstanding, exercisable, and vested and expected to vest as of December 31, 2022:

	Options Outstanding			Weighted-Average Remaining Contractual Term (years)
(In thousands, except per share amounts and years)	Number of Shares	Weighted-Average Exercise Price Per Share			Aggregate Intrinsic Value
Outstanding as of December 31, 2019	1,639,146	$	11.37
Options granted	40,000	$	15.59
Options exercised	(613,119)	$	10.74
Options forfeited	(101,816)	$	19.41
Outstanding as of December 31, 2020	964,211	$	11.08
Options exercised	(360,303)	$	11.06
Options forfeited	(54,327)	$	14.98
Outstanding as of December 31, 2021	549,581	$	10.71
Options exercised	(117,138)	$	7.43
Outstanding as of December 31, 2022	432,443	$	11.60	3.8	$	10,472
Vested or expected to vest at December 31, 2022	432,399	$	11.60	3.8	$	10,471
Options exercisable at December 31, 2022	415,776	$	11.53	3.6	$	10,097

Weighted-average assumptions for stock option plan

The following table presents the weighted-average assumptions used to estimate the fair value of stock options granted that contain only service conditions in the periods presented:

	Stock Option Plan for Year Ended December 31,
	2020
Stock Option Plan
Expected stock price volatility	38%
Risk free interest rate	0.2%
Expected term (in years)	5.5
Weighted-average fair value of stock options granted	$5.46

There were no stock options granted during the years ended December 31, 2022 and 2021, respectively.

Weighted-average assumptions for employee stock purchase plan

	Employee Stock Purchase Plan for Years Ended December 31,
	2022	2021	2020
Employee Stock Purchase Plan
Expected stock price volatility	40%-44%	32%-33%	37%-46%
Risk free interest rate	1.49%-4.58%	0.04%-0.05%	0.1%
Expected term (in years)	0.5	0.5	0.5
Weighted-average fair value of purchase rights granted under the purchase plan	$8.02	$5.17	$3.46

Schedule of nonvested equity stock and stock units activity

The following table reflects the activity related to nonvested equity stock and stock units for the years ended December 31, 2022, 2021 and 2020:

Nonvested Equity Stock and Stock Units	Shares	Weighted-Average Grant-Date Fair Value
Nonvested at December 31, 2019	5,289,483	$	11.27
Granted	1,986,117	$	15.60
Vested	(1,693,659)	$	11.70
Forfeited	(730,676)	$	11.83
Nonvested at December 31, 2020	4,851,265	$	12.82
Granted	2,363,885	$	21.18
Vested	(1,524,950)	$	12.41
Forfeited	(971,815)	$	15.30
Nonvested at December 31, 2021	4,718,385	$	16.62
Granted	2,338,255	$	28.10
Vested	(1,853,260)	$	14.42
Forfeited	(485,320)	$	20.48
Nonvested at December 31, 2022	4,718,060	$	22.78