Note 6 - Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

Notes Tables

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

	Time-Based RSUs					Performance-Based RSUs
				Weighted-Average					Weighted-Average
				Grant Date					Grant Date
	Shares			Fair Value		Shares			Fair Value
Balance at December 31, 2017		221,738			32.72		339,872			33.52
Granted		141,810			43.30		55,455			39.46
Vested		(65,721	)		41.59		(68,459	)		41.22
Forfeited		(12,535	)		35.46		-			-
Balance at September 30, 2018		285,292			35.82		326,868			32.91