Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2016

Summary of Activity Under Stock Option Plans

A summary of the activity under our stock option plans as of June 30, 2016 and changes during the three and six months 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, 2016	198,366		$	40.31	3.3	$	3,934,582
Options exercised	(41,959	)	$	35.60
Options forfeited	(350	)	$	44.32
Options outstanding at June 30, 2016	156,057		$	41.57	3.1	$	3,085,731
Options exercisable at June 30, 2016	156,057		$	41.57	3.1	$	3,085,731
Options vested at June 30, 2016	156,057		$	41.57	3.1	$	3,085,731

	Options Outstanding		Weighted- Average Exercise Price Per Share
Options outstanding at December 31, 2015	212,038		$	40.47
Options exercised	(55,631	)	$	36.99
Options forfeited	(350	)	$	44.32
Options outstanding at June 30, 2016	156,057		$	41.57

Assumptions Used in Calculation of Fair Value

Below were the assumptions used in the Monte Carlo calculation:

	June 30, 2016	June 30, 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	(8,401	)
Non-vested awards outstanding at June 30, 2016	154,651

Time Based Restricted Stock

Restricted Stock Activities

	Time-Based Restricted Stock Awards
Non-vested awards outstanding at December 31, 2015	208,318
Awards granted	117,510
Stock issued	(47,089	)
Awards forfeited	(16,247	)
Non-vested awards outstanding at June 30, 2016	262,492

Deferred Stock Units

Restricted Stock Activities

	Deferred Stock Units
Awards outstanding at December 31, 2015	23,950
Awards granted	11,900
Stock issued	(20,000	)
Awards outstanding at June 30, 2016	15,850