Equity Incentive Plans and Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of shares available for grant

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

	Shares Available  for Grant
Shares available as of December 31, 2018	10,074,046
Stock options granted	—
Stock options forfeited	346,687
Nonvested equity stock and stock units granted (1) (2)	(6,360,359	)
Nonvested equity stock and stock units forfeited (1)	1,146,367
Total available for grant as of June 30, 2019	5,206,741

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

(2)

Amount includes approximately 0.9 million shares that have been reserved for potential future issuance related to certain performance unit awards granted in the first quarter of 2019 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 2015 Plan for the six months ended June 30, 2019 and information regarding stock options outstanding, exercisable, and vested and expected to vest as of June 30, 2019.

	Options Outstanding
	Number of  Shares		Weighted  Average  Exercise Price  Per Share		Weighted  Average  Remaining  Contractual  Term (years)	Aggregate  Intrinsic  Value
	(In thousands, except per share amounts)
Outstanding as of December 31, 2018	3,235,891		$	10.25
Options granted	—		$	—
Options exercised	(924,619	)	$	7.44
Options forfeited	(346,687	)	$	13.86
Outstanding as of June 30, 2019	1,964,585		$	10.93	5.20	$	3,703
Vested or expected to vest at June 30, 2019	1,948,806		$	10.92	5.18	$	3,703
Options exercisable at June 30, 2019	1,535,956		$	10.46	4.34	$	3,703

Weighted-average assumptions for stock option plans

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.

	Equity Incentive Plan
	Three Months Ended June 30, 2018			Six Months Ended June 30, 2018
Stock Options
Expected stock price volatility	24		%	24% - 29%
Risk free interest rate	2.7		%	2.6% - 2.7%
Expected term (in years)	5.8			5.8
Weighted-average fair value of stock options granted to employees	$	3.94		$	4.21

Weighted-average assumptions for employee stock purchase plan

	Employee Stock Purchase Plan
	Six Months Ended
	June 30,
	2019			2018
Employee Stock Purchase Plan
Expected stock price volatility	32		%	27		%
Risk free interest rate	2.44		%	2.05		%
Expected term (in years)	0.5			0.5
Weighted-average fair value of purchase rights granted under the purchase plan	$	2.80		$	3.14

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 six months ended June 30, 2019:

Nonvested Equity Stock and Stock Units	Shares		Weighted-  Average  Grant-Date  Fair Value
Nonvested at December 31, 2018	4,859,135		$	12.71
Granted	3,691,157		$	9.70
Vested	(1,201,894	)	$	12.55
Forfeited	(674,764	)	$	11.63
Nonvested at June 30, 2019	6,673,634		$	11.18