Note 10 - Equity Incentive Plans and Equity (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

	Shares			Weighted-Average Grant-Date Fair Value Per Unit
Outstanding at December 31, 2019		240,229		$	29.07
Granted		55,134			63.68
Issued Upon Vesting		(123,744	)		24.33
Forfeited		(1,328	)		45.32
Outstanding at December 31, 2020		170,291		$	43.60

	Shares		Weighted-Average Grant-Date Fair Value Per Unit
Outstanding at December 31, 2019		-	$	-
Granted		22,894		55.54
Outstanding at December 31, 2020		22,894	$	55.54

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

	Year Ended December 31,
	2020	2019	2018
Weighted average exercise price of options granted	$ 135.55	$ 48.64	$ 27.60
Expected volatility	46.9% - 51.5%	47.6% - 48.5%	48.9% - 50%
Average expected terms in years	5.8 - 7	6 - 6.6	6 - 6.6
Risk-free interest rate	0.3% - 1.69%	2.27%	2.62% - 2.96%
Expected dividend yield	0.0%	0.0%	0.0%

Performance Stock Options [Member]

Notes Tables

Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block]

Options	Shares			Weighted Average Exercise Price		Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2019		1,372,819		$	18.31
Granted		844,508			139.02
Exercised		(63,315	)		27.34
Forfeited		(35,000	)		15.65
Outstanding at December 31, 2020		2,119,012		$	66.19		7.8	$	161,231
Exercisable at December 31, 2020		1,008,964		$	11.05		5.9	$	132,110

Schedule of Nonvested Performance-based Units Activity [Table Text Block]

	Number of Options			Weighted-Average Grant-Date Fair Value Per Share
Nonvested as of December 31, 2019		1,338,361		$	10.89
Granted		844,508			70.83
Vested		(1,037,823	)		6.97
Forfeited		(35,000	)		7.49
Nonvested as of December 31, 2020		1,110,046		$	60.25

Service Period Stock Options [Member]

Notes Tables

Share-based Payment Arrangement, Option, Activity [Table Text Block]

Options	Shares			Weighted Average Exercise Price		Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2019		1,359,990		$	11.50				(Dollars in thousands)
Granted		382,910			127.89
Exercised		(415,499	)		8.97
Forfeited		(357	)		11.00
Outstanding at December 31, 2020		1,327,044		$	45.88		7.0	$	128,778
Exercisable at December 31, 2020		874,153		$	10.99		5.7	$	115,520

Schedule of Nonvested Share Activity [Table Text Block]

	Number of Options			Weighted-Average Grant-Date Fair Value Per Share
Nonvested as of December 31, 2019		347,796		$	8.11
Granted		382,910			64.75
Vested		(277,458	)		6.17
Forfeited		(357	)		5.61
Nonvested as of December 31, 2020		452,891		$	57.19