Note 8 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

Notes Tables

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

	Stock Options			Weighted- Average Exercise Price
Options outstanding at December 31, 2015		766,042		$	36.52
Granted		113,645			58.12
Exercised		(173,781	)		18.42
Forfeited		(69,965	)		61.37
Options outstanding at September 30, 2016		635,941		$	42.59
Exercisable at September 30, 2016		368,052		$	31.13

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Nine Months Ended September 30,
	2016			2015
Risk-free interest rate	1.53	-	1.68%	1.69	-	1.77%
Expected life (years)		6.50		5.50	-	6.50
Expected volatility	44.38	-	45.93%	46.80	-	47.23%
Expected dividend yield		0%			0%

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

				Weighted-
				Average
				Grant Date
	Restricted			Fair Value
	Stock			Per Share
Restricted stock at December 31, 2015		124,393		$	68.97
Granted		159,705			59.43
Restrictions lapsed		(40,779	)		67.85
Forfeited		(19,645	)		63.99
Restricted stock at September 30, 2016		223,674		$	62.80

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

	Nine Months Ended September 30,
	2016			2015
Risk-free interest rate	0.39	-	0.56%	0.08	-	0.10%
Expected life (months)		6.00			6.00
Expected volatility	29.41	-	49.13%	33.68	-	37.64%
Expected dividend yield		0%			0%