Equity Incentive Plans and Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2017

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, 2016	7,305,368
Stock options granted	(498,426	)
Stock options forfeited	1,472,366
Nonvested equity stock and stock units granted (1) (2)	(3,553,590	)
Nonvested equity stock and stock units forfeited (1)	714,375
Total available for grant as of June 30, 2017	5,440,093

_________________________________________


(1)	For purposes of determining the number of shares available for grant under 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 266,847 shares that have been reserved for potential future issuance related to certain performance unit awards granted in the first quarter of 2017 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 2006 Plan and 2015 Plan for the six months ended June 30, 2017 and information regarding stock options outstanding, exercisable, and vested and expected to vest as of June 30, 2017.



	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, 2016	7,008,833		$	9.34
Options granted	498,426		$	12.74
Options exercised	(654,388	)	$	7.04
Options forfeited	(1,472,366	)	$	10.95
Outstanding as of June 30, 2017	5,380,505		$	9.49	5.48	$	16,061
Vested or expected to vest at June 30, 2017	5,297,443		$	9.45	5.43	$	16,037
Options exercisable at June 30, 2017	3,874,169		$	9.20	4.58	$	13,287

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 Plan
	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2017			2016			2017			2016
Stock Option Plan
Expected stock price volatility	32		%	—		%	32		%	36		%
Risk free interest rate	1.8		%	—		%	1.8% - 1.9%			1.7		%
Expected term (in years)	5.3			—			5.3 - 5.4			6.1
Weighted-average fair value of stock options granted to employees	$	3.84		$	—		$	4.12		$	4.66

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, 2017:



Nonvested Equity Stock and Stock Units	Shares		Weighted- Average Grant-Date Fair Value
Nonvested at December 31, 2016	4,863,056		$	12.33
Granted	2,191,162		$	12.81
Vested	(615,671	)	$	11.59
Forfeited	(450,339	)	$	12.54
Nonvested at June 30, 2017	5,988,208		$	12.57

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]



	Employee Stock Purchase Plan
	Six Months Ended
	June 30,
	2017			2016
Employee Stock Purchase Plan
Expected stock price volatility	27		%	33		%
Risk free interest rate	0.98		%	0.41		%
Expected term (in years)	0.5			0.5
Weighted-average fair value of purchase rights granted under the purchase plan	$	2.87		$	2.86