Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2014

Summary of Activity Under Stock Option Plans

A summary of the activity under our stock option plans as of June 30, 2014 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, 2014	656,506		$	42.44	4.1	$	13,184,080
Options granted	—		—
Options exercised	(79,744	)	48.10
Options forfeited	(20,150	)	59.85
Options outstanding at June 30, 2014	556,612		40.96		4.3	14,132,906
Options exercisable at June 30, 2014	480,443		40.24		3.8	12,543,846
Options vested or expected to vest at June 30, 2014*	554,327		40.94		4.3	14,085,234

* 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, 2013	893,139		$	40.58
Options granted	—		—
Options exercised	(315,627	)	46.12
Options forfeited	(20,900	)	59.16
Options outstanding at June 30, 2014	556,612

Assumptions Used in Calculation of Fair Value

Below are the assumptions used in the Monte Carlo calculation:

	June 30, 2014	June 30, 2013
Expected volatility	33.7%	37.1%
Expected term (in years)	3.0	3.0
Risk-free interest rate	0.67%	0.40%
Expected dividend yield	—	—

Performance-Based Restricted Stock [Member]

Restricted Stock Activities

	Performance-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2013	71,175
Awards granted	49,700
Stock issued	(14,383	)
Awards forfeited	(5,250	)
Non-vested awards outstanding at June 30, 2014	101,242

Time Based Restricted Stock [Member]

Restricted Stock Activities

	Time-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2013	231,026
Awards granted	66,380
Stock issued	(46,712	)
Awards forfeited	(2,775	)
Non-vested awards outstanding at June 30, 2014	247,919

Deferred Stock Units [Member]

Restricted Stock Activities

	Deferred Stock Units
Awards outstanding at December 31, 2013	31,550
Awards granted	13,600
Stock issued	(14,400	)
Awards outstanding at June 30, 2014	30,750