Note 8 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2015

Notes Tables

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

				Weighted-
				Average
	Stock Options			Exercise Price
Options outstanding at December 31, 2014		998,987		$	26.49
Granted		110,335			67.36
Exercised		(86,656	)		15.72
Forfeited		(25,713	)		52.39
Options outstanding at June 30, 2015		996,953		$	31.28
Exercisable at June 30, 2015		515,568		$	19.12

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

	Six Months Ended June 30,
	2015			2014
Risk-free interest rate	1.69	-	1.77%	0.43	-	2.14%
Expected life (years)	5.50	-	6.50	2.00	-	6.50
Expected volatility	46.80	-	47.23%	48.87	-	49.30%
Expected dividend yield		0%			0%

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

				Weighted-
				Average
				Grant Date
	Restricted			Fair Value
	Stock			Per Share
Nonvested restricted stock at December 31, 2014		76,574		$	69.27
Granted		68,580			68.89
Vested		(16,161	)		69.47
Forfeited		(1,858	)		78.59
Nonvested restricted stock at June 30, 2015		127,135		$	68.90

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

	Six Months Ended June 30,
	2015			2014
Risk-free interest rate	0.08	-	0.10%	0.01	-	0.11%
Expected life (months)		6.00			6.00
Expected volatility	33.68	-	37.64%	39.16	-	39.80%
Expected dividend yield		0%			0%