Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2016

Summary of Activity Under Stock Option Plans

A summary of the activity under our stock option plans as of March 31, 2016 and changes during the quarter 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, 2015	212,038		$	40.47	3.2	$	2,557,193
Options exercised	(13,672	)	$	41.25
Options forfeited	—		$	—
Options outstanding at March 31, 2016	198,366		$	40.31	3.3	$	3,934,582
Options exercisable at March 31, 2016	198,366		$	40.31	3.3	$	3,934,582
Options vested at March 31, 2016	198,366		$	40.31	3.3	$	3,934,582

Assumptions Used in Calculation of Fair Value

Below were the assumptions used in the Monte Carlo calculation:

	March 31, 2016	March 31, 2015
Expected volatility	29.6%	28.2%
Expected term (in years)	3.0	3.0
Risk-free interest rate	0.93%	0.96%

Performance-Based Restricted Stock

Restricted Stock Activities

	Performance-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2015	107,229
Awards granted	81,220
Stock issued	(25,397	)
Awards forfeited	(5,431	)
Non-vested awards outstanding at March 31, 2016	157,621

Time Based Restricted Stock

Restricted Stock Activities

	Time-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2015	208,318
Awards granted	116,610
Stock issued	(46,429	)
Awards forfeited	(11,309	)
Non-vested awards outstanding at March 31, 2016	267,190

Deferred Stock Units

Restricted Stock Activities

	Deferred Stock Units
Awards outstanding at December 31, 2015	23,950
Awards granted	—
Stock issued	(1,650	)
Awards outstanding at March 31, 2016	22,300