Note 19 - Equity Incentive Plans - Restricted Stock Units (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Time-based Restricted Stock Units [Member]
Balance (in shares)	221,738	152,476	85,111
Balance, weighted-average grant date fair value (in dollars per share)	$ 32.72	$ 28.89	$ 27.55
Granted (in shares)	141,810	87,781	88,693
Granted, weighted-average grant date fair value (in dollars per share)	$ 43.30	$ 38.59	$ 30.37
Vested (in shares)	(65,721)	(1,167)	(13,780)
Vested, weighted-average grant date fair value (in dollars per share)	$ 41.59	$ 38.03	$ 29.80
Forfeited (in shares)	(13,334)	(17,352)	(7,548)
Forfeited, weighted-average grant date fair value (in dollars per share)	$ 35.96	$ 33.10	$ 29.49
Balance (in shares)	284,493	221,738	152,476
Balance, weighted-average grant date fair value (in dollars per share)	$ 35.79	$ 32.72	$ 28.89
Performance-based Restricted Stock Units [Member]
Balance (in shares)	339,872	574,943	457,264
Balance, weighted-average grant date fair value (in dollars per share)	$ 33.52	$ 28.96	$ 26.84
Granted (in shares)	55,455	159,264	117,679
Granted, weighted-average grant date fair value (in dollars per share)	$ 39.46	$ 40.36	$ 37.22
Vested (in shares)	(121,336)	(394,335)
Vested, weighted-average grant date fair value (in dollars per share)	$ 37.87	$ 39.96
Forfeited (in shares)	(8,332)
Forfeited, weighted-average grant date fair value (in dollars per share)	$ 29.61
Balance (in shares)	265,659	339,872	574,943
Balance, weighted-average grant date fair value (in dollars per share)	$ 32.90	$ 33.52	$ 28.96