Note 15 - Stock-based Compensation - Summary of the Status of the 2012 Incentive Plan (Details) - $ / shares shares in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Outstanding at beginning of year (in shares)		2,527
Outstanding at end of year (in shares)		1,792	2,527
2012 Incentive Plan [Member]
Outstanding at beginning of year (in shares)		2,527	1,548	2,565
Outstanding at beginning of year (in dollars per share)		$ 46.77	$ 41.35	$ 33.36
Stock Options (in shares)		0	0	30
Stock Options (in dollars per share)		$ 0	$ 0	$ 57.97
Exercised (in shares)		(711)	(203)	(1,181)
Exercised (in dollars per share)		$ 37.83	$ 29.75	$ 25.92
Forfeited (in shares)		(71)	(64)	(21)
Forfeited (in dollars per share)		$ 50.59	$ 45.73	$ 46.15
Expired (in shares)		0	0	0
Expired (in dollars per share)		$ 0	$ 0	$ 0
Outstanding at end of year (in shares)		1,792	2,527	1,548
Outstanding at end of year (in dollars per share)		$ 50.39	$ 46.77	$ 41.35
Options and SARs exercisable at end of year (in shares)		479	846	431
Options and SARs exercisable at end of year (in dollars per share)		$ 48.35	$ 42.06	$ 32.61
Weighted-average fair value of options and SARs granted during the year (in dollars per share)		$ 29.24	$ 16.45	$ 22.82
2012 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member]
Other than Options (in shares)	[1]	38	1,172	132
Other than Options (in dollars per share)	[1]	$ 69.13	$ 53.87	$ 62.55
2012 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Other than Options (in shares)	[2]	9	74	23
Other than Options (in dollars per share)	[2]	$ 0	$ 0	$ 0

[1] Upon exercise, SARs entitle the recipient to receive shares of common stock equal to the increase in value of the award between the grant date and the exercise date.

[2] An RSU represents the right to receive one share of common stock once certain vesting conditions are met. The value of an RSU is identical to the value of the underlying stock.