Stock-Based Compensation (Tables)

he fair values of the 2013 awards was estimated using Monte-Carlo simulation with the following weighted-average assumptions.



	For the Three Months Ended
	March 31, 2013

Expected dividend yield	—	%
Risk-free interest rate ⁽¹⁾	0.35	%
Expected volatility ⁽²⁾	30.59	%
Average total shareholder return ⁽²⁾	8.21	%


(1)	The risk-free interest rate for the periods within the contractual term of the options is based on the U.S. Treasury yield curve in effect at the time of the grant.


(2)	The expected volatility and average total shareholder return is a measure of the amount by which a stock price has fluctuated or is expected to fluctuate based primarily on our and our peers' historical data.


(3)	The expected life is the period of time, on average, that participants are expected to hold their options before exercise based primarily on our historical data.

The fair values of these stock options were estimated using the Black-Scholes valuation model with the following weighted-average assumptions:


(1)	The risk-free interest rate for the periods within the contractual term of the options is based on the U.S. Treasury yield curve in effect at the time of the grant.


(2)	The expected volatility is a measure of the amount by which a stock price has fluctuated or is expected to fluctuate based primarily on our and our peers' historical data.


(3)	The expected life is the period of time, on average, that participants are expected to hold their options before exercise based primarily on our historical data.

RSU activity for the three months ended March 31, 2013 is as follows:



	Number of		Weighted Average Grant-Date
(in thousands, except weighted average fair value prices)	Shares		Fair Value
Unvested RSUs outstanding at December 31, 2012	1,381		$	17.50
RSUs granted	593		$	26.11
RSUs vested	(450	)	$	17.21
RSUs forfeited	(7	)	$	18.20
Unvested RSUs outstanding at March 31, 2013	1,517		$	20.95

PBRSU activity for the three months ended March 31, 2013, is as follows:



	Number of		Weighted Average Grant-Date
(in thousands, except weighted average fair value prices)	Shares		Fair Value
Unvested PBRSUs outstanding at December 31, 2012	1,151		$	17.21
PBRSUs granted	390		$	26.02
PBRSUs vested	(157	)	$	18.18
PBRSUs forfeited	(23	)	$	17.73
Unvested PBRSUs outstanding at March 31, 2013	1,361		$	18.40

Option activity for the three months ended March 31, 2013 is as follows:



(in thousands, except weighted average price)	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Options outstanding at December 31, 2012	3,765		$	20.18
Options granted	403		$	26.02
Options exercised	(207	)	$	20.63
Options canceled	(56	)	$	17.70
Options outstanding at March 31, 2013	3,905		$	20.79	5.8	$	20,455
Options vested and expected to vest at March 31, 2013	3,647		$	20.58	5.6	$	19,875
Options exercisable at March 31, 2013	2,381		$	21.64	4.1	$	10,651

The following table sets forth the stock-based compensation expense recognized for the three months ended March 31, 2013 and 2012.



	For the Three Months Ended
	March 31,
(in thousands)	2013		2012
RSUs	5,100		2,213
PBRSUs	2,155		1,360
Stock options	683		781
Employee stock purchase plan	204		—
	$	8,142	$	4,354