Stock Options And Employee Stock Purchase Plan (Tables)

9 Months Ended

Sep. 30, 2016

The following table represents stock option activity for the nine months ended September 30, 2016:



	Number of Shares		Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at January 1, 2016	566,428		$	29.74
Granted	—		—
Exercised	(132,073	)	25.91
Canceled	(9,700	)	26.92
Outstanding at September 30, 2016	424,655		$	31.00	4.1	$	15,169,195
Exercisable at September 30, 2016	362,555		$	26.12	3.4	$	14,688,225
Vested and expected to vest at September 30, 2016	412,053		$	29.96	3.9	$	15,137,035

The weighted-average fair values of market-based restricted stock awards granted have been estimated utilizing the following assumptions:



	September 30, 2016
Underlying stock price at valuation date	$	63.73
Expected volatility	29.8		%
Risk-free interest rate	1.51		%

Restricted stock award activity for the nine months ended September 30, 2016 is set forth below:



	Shares		Weighted-Average Grant-Date Fair Value
Nonvested at January 1, 2016	704,804		$	39.08
Granted	291,914		40.82
Vested	(159,035	)	44.53
Canceled	(34,700	)	66.31
Nonvested at September 30, 2016	802,983		$	37.46

Restricted stock unit award activity for the nine months ended September 30, 2016 is set forth below:



	Number of Shares		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at January 1, 2016	56,245
Granted	21,250
Vested	(10,755	)
Canceled	(11,200	)
Outstanding at September 30, 2016	55,540		1.9	$	3,699,519
Vested and expected to vest at September 30, 2016	43,475		1.7	$	2,895,863