Note 6 - Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Years ended December 31,
	2019		2018		2017
Restricted share units
Pretax compensation expense	$	38,632	$	32,797	$	28,679
Tax benefit		9,337		7,740		(4,385	)
Restricted share units, net of tax	$	29,295	$	25,057	$	33,064
Performance share units
Pretax compensation expense	$	14,692	$	14,572	$	9,612
Tax benefit		3,551		3,439		(1,470	)
Performance share awards, net of tax	$	11,141	$	11,133	$	11,082

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

Restricted Share Units	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2016		1,502,656		$	71.16
Granted		158,319			90.06
Vested		(380,702	)		67.29
Forfeited		(37,745	)		75.13
Unvested at December 31, 2017		1,242,528		$	74.71
Granted		370,669			119.82
Vested		(337,512	)		79.02
Forfeited		(29,850	)		83.69
Unvested at December 31, 2018		1,245,835		$	86.80
Granted		440,255			99.60
Vested		(341,218	)		85.61
Forfeited		(31,454	)		93.91
Unvested at December 31, 2019		1,313,418		$	91.22

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

Performance Share Units	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2016		484,054		$	70.58
Granted		-			-
Vested		(155,867	)		68.27
Forfeited		-			-
Unvested at December 31, 2017		328,187		$	71.68
Granted		150,763			122.57
Vested		(118,438	)		69.29
Forfeited		-			-
Unvested at December 31, 2018		360,512		$	93.74
Granted		142,156			98.58
Vested		(127,140	)		93.46
Forfeited		-			-
Unvested at December 31, 2019		375,528		$	95.67