Note 17 - Earnings Per Share Reconciliation (Details) - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Class A [Member] | Distributed [Member]
Reallocation of distributed income as a result of conversion of dilutive stock options	$ 15,000	$ 15,000	$ 15,000
Reallocation of distributed income due to conversion of Class B to Class A	1,932,000	1,547,000	1,009,000
Common Class A [Member] | Diluted [Member]
Distributed income applicable to common stockholders	(19,985,000)	(15,929,000)	(10,085,000)
Distributed income applicable to common stockholders	19,985,000	15,929,000	10,085,000
Undistributed income from continuing operations applicable to common stockholders	163,014,000	119,611,000	95,129,000
Common Class A [Member] | Undistributed [Member]
Reallocation of distributed income as a result of conversion of dilutive stock options	120,000	116,000	142,000
Reallocation of distributed income due to conversion of Class B to Class A	$ 15,760,000	$ 11,616,000
Common Class A [Member] | Employee Stock Option [Member]
Shares issuable pursuant to stock options not included since they were antidilutive (in shares)	16	13
Common Class A [Member]
Income from continuing operations applicable to common stockholders	$ 165,172,000	$ 122,246,000	94,532,000
Distributed income applicable to common stockholders	(18,038,000)	(14,367,000)	(9,061,000)
Basic undistributed income from continuing operations applicable to common stockholders	$ 147,134,000	$ 107,879,000	$ 85,471,000
Weighted average number of shares out-standing used to calculate basic income per share (in shares)	23,729	23,559	23,185
Basic income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.96	$ 5.19	$ 4.08
Basic distributed income per share applicable to common stockholders (in dollars per share)	(0.76)	(0.61)	(0.39)
Basic undistributed income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.20	$ 4.58	$ 3.69
Distributed income applicable to common stockholders	$ 18,038,000	$ 14,367,000	$ 9,061,000
Undistributed income from continuing operations applicable to common stockholders	$ 147,134,000	$ 107,879,000	$ 85,471,000
Weighted average number of shares from stock options (in shares)	200	261	386
Conversion of Class B to Class A (in shares)	2,561	2,562	2,620
Weighted average number of shares outstanding used to calculate diluted income per share (in shares)	26,490	26,382	26,191
Diluted income from continuing operations per share available to common stockholders	$ 6,910	$ 5,140	$ 4,020
Diluted distributed income from continuing operations per share applicable to common stockholders (in dollars per share)	$ (0.76)	$ (0.61)	$ (0.39)
Diluted undistributed income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.15	$ 4.53	$ 3.63
Common Class B [Member] | Distributed [Member]
Reallocation of distributed income as a result of conversion of dilutive stock options	$ (15,000)	$ (15,000)	$ (15,000)
Reallocation of distributed income due to conversion of Class B to Class A
Common Class B [Member] | Diluted [Member]
Distributed income applicable to common stockholders	$ (1,932,000)	$ (1,547,000)	$ (1,009,000)
Distributed income applicable to common stockholders	1,932,000	1,547,000	1,009,000
Undistributed income from continuing operations applicable to common stockholders	15,760,000	11,616,000	9,516,000
Common Class B [Member] | Undistributed [Member]
Reallocation of distributed income as a result of conversion of dilutive stock options	(120,000)	(116,000)	(142,000)
Common Class B [Member]
Income from continuing operations applicable to common stockholders	17,827,000	13,294,000	10,682,000
Distributed income applicable to common stockholders	(1,947,000)	(1,562,000)	(1,024,000)
Basic undistributed income from continuing operations applicable to common stockholders	$ 15,880,000	$ 11,732,000	$ 9,658,000
Weighted average number of shares out-standing used to calculate basic income per share (in shares)	2,561	2,562	2,620
Basic income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.96	$ 5.19	$ 4.08
Basic distributed income per share applicable to common stockholders (in dollars per share)	(0.76)	(61)	(0.39)
Basic undistributed income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.20	$ 4.58	$ 3.69
Distributed income applicable to common stockholders	$ 1,947,000	$ 1,562,000	$ 1,024,000
Undistributed income from continuing operations applicable to common stockholders	$ 15,880,000	$ 11,732,000	$ 9,658,000
Weighted average number of shares from stock options (in shares)
Conversion of Class B to Class A (in shares)
Weighted average number of shares outstanding used to calculate diluted income per share (in shares)	2,561	2,562	2,620
Diluted income from continuing operations per share available to common stockholders	$ 6,910	$ 5,140	$ 4,020
Diluted distributed income from continuing operations per share applicable to common stockholders (in dollars per share)	$ (0.76)	$ (0.61)	$ (0.39)
Diluted undistributed income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.15	$ 4.53	$ 3.63
Income from continuing operations applicable to common stockholders	$ 182,999,000	$ 135,540,000	$ 105,214,000
Weighted average number of shares out-standing used to calculate basic income per share (in shares)	26,290	26,121	25,805
Basic income from continuing operations per share applicable to common stockholders (in dollars per share)	$ 6.96	$ 5.19	$ 4.08
Weighted average number of shares outstanding used to calculate diluted income per share (in shares)	26,490	26,382	26,191