Note 4 - Earnings Per Share - Earnings Per Share Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator for basic and diluted earnings per share – Net income available to common shareholders	$ 33,939	$ 39,104	$ 73,862	$ 117,829
Denominator for basic earnings per share – weighted average shares outstanding (in shares)	55,033	54,817	54,734	55,116
Effect of dilutive securities– Employee and director stock options and restricted share awards (in shares)	1,410	1,209	1,195	1,322
Denominator for diluted earnings per share – adjusted weighted average shares outstanding and assumed conversions (in shares)	56,443	56,026	55,929	56,438
Basic earnings per common share (in dollars per share)	$ 0.62	$ 0.71	$ 1.35	$ 2.14
Diluted earnings per common share and common share equivalents (in dollars per share)	$ 0.60	$ 0.70	$ 1.32	$ 2.09