Equity Incentive Plans and Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2016

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

Shares available for grant under stock-based incentive plans

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



	Shares Available for Grant
Shares available as of December 31, 2015	11,173,545
Stock options granted	(440,000	)
Stock options forfeited	470,134
Stock options expired under former plans	(192,467	)
Nonvested equity stock and stock units granted (1) (2)	(3,060,279	)
Nonvested equity stock and stock units forfeited (1)	457,911
Total available for grant as of March 31, 2016	8,408,844

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(1)	For purposes of determining the number of shares available for grant under the 2015 Plan (and previously the 2006 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 300,003 shares that have been reserved for potential future issuance related to certain performance unit awards granted in the first quarter of 2016 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 1997 Plan, 2006 Plan and 2015 Plan for the three months ended March 31, 2016 and information regarding stock options outstanding, exercisable, and vested and expected to vest as of March 31, 2016.



	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, 2015	8,995,017		$	10.01
Options granted	440,000		$	12.31
Options exercised	(550,229	)	$	6.82
Options forfeited	(470,134	)	$	15.02
Outstanding as of March 31, 2016	8,414,654		$	10.06	5.75	$	43,807
Vested or expected to vest at March 31, 2016	8,129,382		$	10.12	5.68	$	42,263
Options exercisable at March 31, 2016	5,139,627		$	11.39	4.66	$	24,873

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.



	Stock Option Plans
	Three Months Ended
	March 31,
	2016			2015
Stock Option Plans
Expected stock price volatility	36		%	41		%
Risk free interest rate	1.7		%	1.2		%
Expected term (in years)	6.1			6.0
Weighted-average fair value of stock options granted to employees	$	4.66		$	4.59

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 three months ended March 31, 2016:



Nonvested Equity Stock and Stock Units	Shares		Weighted- Average Grant-Date Fair Value
Nonvested at December 31, 2015	3,008,118		$	11.32
Granted	1,840,184		$	12.33
Vested	(362,963	)	$	10.04
Forfeited	(164,864	)	$	11.61
Nonvested at March 31, 2016	4,320,475		$	11.85