Note 6 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

Notes Tables

Share-based Payment Arrangement, Restricted Stock Unit, 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, 2018		284,493		$	35.79		265,659		$	32.90
Granted		18,818			38.36		35,092			38.36
Vested		(92,868	)		35.12		(92,501	)		38.36
Forfeited		(16,672	)		38.31		—			—
Balance at June 30, 2019		193,771		$	36.14		208,250		$	31.39