Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value of Options Granted Calculated Using Weighted Average Assumptions

Below are the assumptions used in the Monte Carlo calculation:

Expected volatility	37.1	%
Expected term (in years)	3.0
Risk-free interest rate	0.40	%
Expected dividend yield	—

The fair value of options granted during the three month period ended March 31, 2012 were calculated using the following weighted-average assumptions: 

	March 31, 2012
Options granted	46,950
Weighted average exercise price	$	41.27
Weighted-average grant date fair value	19.08
Assumptions:
Expected volatility	47.70		%
Expected term (in years)	5.9
Risk-free interest rate	1.43		%
Expected dividend yield	—

Summary of Activity Under Stock Option Plans

A summary of the activity under our stock option plans as of March 31, 2013 and changes during the three month period then ended, is presented below:

	Options Outstanding		Weighted- Average Exercise Price Per Share		Weighted-Average Remaining Contractual Life in Years	Aggregate Intrinsic Value
Options outstanding at December 31, 2012	1,765,947		$	40.58	5.0	$	12,195,931
Options granted	—		—
Options exercised	(95,183	)	32.19
Options cancelled	(117	)	24.20
Options outstanding at March 31, 2013	1,670,647		41.06		4.3	15,558,730
Options exercisable at March 31, 2013	1,326,398		42.40		3.5	11,452,910
Options vested or expected to vest at March 31, 2013*	1,660,320		41.09		4.2	15,435,555

* In addition to the vested options, we expect a portion of the unvested options to vest at some point in the future.  Options expected to vest are calculated by applying an estimated forfeiture rate to the unvested options.

Performance-Based Restricted Stock [Member]

Restricted Stock Activities

	Performance-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2012	73,458
Awards granted	48,660
Stock issued	(33,538	)
Awards forfeited	(1,062	)
Non-vested awards outstanding at March 31, 2013	87,518

Time Based Restricted Stock [Member]

Restricted Stock Activities

	Time-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2012	115,139
Awards granted	63,200
Stock issued	(124	)
Awards forfeited	(396	)
Non-vested awards outstanding at March 31, 2013	177,819

Deferred Stock Units [Member]

Restricted Stock Activities

	Deferred Stock Units
Awards outstanding at December 31, 2012	30,150
Awards granted	—
Stock issued	—
Awards outstanding at March 31, 2013	30,150