Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2013

Fair Value of Options Granted Calculated Using Weighted Average Assumptions

The fair value of options granted during the nine month period ended September 30, 2012 were calculated using the following weighted-average assumptions: 

	September 30, 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	—

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	—

Summary of Activity Under Stock Option Plans

A summary of the activity under our stock option plans as of September 30, 2013 and changes during the three and nine month periods 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 June 30, 2013	1,503,873		$	42.26	3.7	$	12,388,067
Options granted	—		—
Options exercised	(461,081	)	38.94
Options forfeited	(13,617	)	42.43
Options outstanding at September 30, 2013	1,029,175		43.75		3.9	16,452,670
Options exercisable at September 30, 2013	831,692		45.32		3.2	12,038,245
Options vested or expected to vest at September 30, 2013*	1,023,251		43.78		3.9	16,320,237

* 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.

	Options Outstanding		Weighted- Average Exercise Price Per Share
Options outstanding at December 31, 2012	1,765,947		$	40.58
Options granted	—		—
Options exercised	(712,321	)	36.04
Options forfeited	(24,451	)	39.49
Options outstanding at September 30, 2013	1,029,175

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	(15,222	)
Non-vested awards outstanding at September 30, 2013	73,358

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	152,380
Stock issued	(7,136	)
Awards forfeited	(24,492	)
Non-vested awards outstanding at September 30, 2013	235,891

Deferred Stock Units [Member]

Restricted Stock Activities

	Deferred Stock Units
Awards outstanding at December 31, 2012	30,150
Awards granted	16,800
Stock issued	(15,400	)
Awards outstanding at September 30, 2013	31,550