Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 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 six month period ended June 30, 2012 were calculated using the following weighted-average assumptions: 

	June 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	—

Summary of Activity Under Stock Option Plans

A summary of the activity under our stock option plans as of June 30, 2013 and changes during the three and six 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 March 31, 2013	1,670,647		$	41.06	4.3	$	15,558,730
Options granted	—		—
Options exercised	(156,057	)	29.80
Options cancelled	(10,717	)	36.17
Options outstanding at June 30, 2013	1,503,873		42.26		3.7	12,388,067
Options exercisable at June 30, 2013	1,201,313		43.66		2.9	9,078,139
Options vested or expected to vest at June 30, 2013*	1,494,796		42.29		3.7	12,288,769

* 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	(251,240	)	30.71
Options cancelled	(10,834	)	36.05
Options outstanding at June 30, 2013	1,503,873

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	(11,502	)
Non-vested awards outstanding at June 30, 2013	77,078

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	(18,297	)
Non-vested awards outstanding at June 30, 2013	159,918

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 June 30, 2013	31,550