Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2015

Presented below is a summary of our stock option activity for the six months ended June 30, 2015 (in thousands, except for weighted average exercise price and weighted average remaining contractual terms):

	Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Terms	Aggregate Intrinsic Value

Outstanding at December 31, 2014	4,101		$	18.72
Granted	1,254		16.78
Exercised	(472	)	7.23
Forfeited	(335	)	22.85
Expired	(272	)	25.74

Outstanding at June 30, 2015	4,276		18.65		4.97	$	7,249

Expected to vest at June 30, 2015	2,611		19.57		6.16	489
Exercisable at June 30, 2015	1,606		$	17.13	3.00	$	6,750

Schedule of weighted -average assumptions used for estimating fair value of each stock option grant on the date of grant

	Six months ended June 30,
	2015		2014
Expected dividend yield	—		—
Risk-free interest rate	1.65	%	1.50	%
Expected volatility	38.28	%	37.27	%
Expected life	4.89 years		4.81 years

Summary of status of restricted stock units

A summary of the status of our restricted stock units and of changes in restricted stock units outstanding under the 2006 Stock Plan for the six months ended June 30, 2015 is as follows (in thousands, except for weighted average grant date fair value per unit):

	Number of Units		Weighted Average Grant Date Fair Value per Unit
Outstanding balance at December 31, 2014	910		$	22.84
Granted	660		16.75
Vesting of restricted stock units, net of shares withheld for taxes	(95	)	24.07
Shares withheld for taxes	(36	)	24.07
Forfeitures	(107	)	23.92

Outstanding balance at June 30, 2015	1,332		$	19.61