Share-Based Compensation Plans (Tables)

The RSU awards will vest ratably over 3 years. RSU activity for the year ended December 31, 2015 is as follows:



(in thousands, except weighted average fair value prices)	Number of Shares		Weighted Average Grant-Date Fair Value
Unvested RSUs outstanding at December 31, 2014	1,380		$	27.17
RSUs granted	966		$	35.31
RSUs vested	(715	)	$	25.19
RSUs forfeited	(94	)	$	31.81
Unvested RSUs outstanding at December 31, 2015	1,537		$	32.92

The fair values of the 2015 and 2014 awards were estimated using Monte-Carlo simulation with the following weighted-average assumptions:



	2015		2014		2013

Expected dividend yield	—	%	—	%	—	%
Risk-free interest rate ⁽¹⁾	0.93	%	0.74	%	0.41	%
Expected volatility ⁽²⁾	24.01	%	27.88	%	29.87	%
Average total shareholder return ⁽²⁾	8.37	%	(0.90	)%	17.87	%


(1)	The risk-free interest rate for the periods within the contractual term of the PBRSUs 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.

PBRSU activity for the year ended December 31, 2015 is as follows:



(in thousands, except weighted average fair value prices)	Number of Shares		Weighted Average Grant-Date Fair Value
Unvested PBRSUs outstanding at December 31, 2014	904		$	22.19
PBRSUs granted	232		$	34.01
PBRSUs vested	(415	)	$	16.51
PBRSUs forfeited	(62	)	$	30.63
Unvested PBRSUs outstanding at December 31, 2015	659		$	29.15

he fair values of these stock options were estimated using a Black-Scholes 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.

Option activity for the year ended December 31, 2015 is as follows:



(in thousands, except weighted average prices)	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Options outstanding at December 31, 2014	2,563		$	22.32
Options granted	—		$	—
Options exercised	(695	)	$	24.53
Options canceled	(42	)	$	28.62
Options outstanding at December 31, 2015	1,826		$	21.33	5.1	$	22,867
Options vested and expected to vest at December 31, 2015	1,818		$	21.30	5.1	$	22,849
Options exercisable at December 31, 2015	1,579		$	20.09	4.7	$	21,756

The following table sets forth the share-based compensation expense recognized for the years ended December 31, 2015, 2014 and 2013:



(in thousands)	2015		2014		2013
Restricted stock units	$	24,591	$	19,078	$	12,754
Performance-based restricted stock units	8,080		1,750		9,746
Stock options	1,923		3,730		3,982
Employee stock purchase plan	1,192		1,030		557
	$	35,786	$	25,588	$	27,039