Note 17 - Net Income Per Share of Class A and Class B Common Stock (Details) - Earnings Per Share Reconciliation (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Income from continuing operations applicable to common stockholders	$ 135,540,000	$ 105,214,000	$ 79,395,000
Denominator:
Weighted average number of shares out-standing used to calculate basic income per share (in Shares)	26,121	25,805	25,696
Basic income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 5.19	$ 4.08	$ 3.09
Denominator:
Weighted average number of shares outstanding used to calculate basic income per share (in Shares)	26,121	25,805	25,696
Weighted average number of shares outstanding used to calculate diluted income per share (in Shares)	26,382	26,191	26,170
Common Class A [Member] \| Equity Option [Member]
Antidilutive Securities:
Shares issuable pursuant to stock options not included since they were antidilutive (in Shares)	13	16	45
Common Class A [Member] \| Basic [Member]
Numerator:
Distributed income applicable to common stockholders	(14,367,000)	(9,061,000)	(10,497,000)
Numerator:
Distributed income applicable to common stockholders	14,367,000	9,061,000	10,497,000
Diluted distributed income applicable to common stockholders	14,367,000	9,061,000	10,497,000
Common Class A [Member] \| Distributed [Member]
Numerator:
Reallocation of distributed income as a result of conversion of dilutive stock options	15,000	15,000	28,000
Reallocation of distributed income due to conversion of Class B to Class A	1,547,000	1,009,000	1,541,000
Reallocation of undistributed income as a result of conversion of dilutive stock options	15,000	15,000	28,000
Reallocation of undistributed income due to conversion of Class B to Class A	1,547,000	1,009,000	1,541,000
Common Class A [Member] \| Diluted [Member]
Numerator:
Distributed income applicable to common stockholders	(15,929,000)	(10,085,000)	(12,066,000)
Numerator:
Distributed income applicable to common stockholders	15,929,000	10,085,000	12,066,000
Diluted distributed income applicable to common stockholders	15,929,000	10,085,000	12,066,000
Undistributed income from continuing operations applicable to common stockholders	119,611,000	95,129,000	67,329,000
Diluted undistributed income from continuing operations applicable to common stockholders	119,611,000	95,129,000	67,329,000
Common Class A [Member] \| Undistributed [Member]
Numerator:
Reallocation of distributed income as a result of conversion of dilutive stock options	116,000	142,000	159,000
Reallocation of distributed income due to conversion of Class B to Class A	11,616,000	9,516,000	8,598,000
Reallocation of undistributed income as a result of conversion of dilutive stock options	116,000	142,000	159,000
Reallocation of undistributed income due to conversion of Class B to Class A	11,616,000	9,516,000	8,598,000
Common Class A [Member]
Numerator:
Income from continuing operations applicable to common stockholders	122,246,000	94,532,000	69,069,000
Distributed income applicable to common stockholders	(14,367,000)	(9,061,000)	(10,497,000)
Basic undistributed income from continuing operations applicable to common stockholders	107,879,000	85,471,000	58,572,000
Denominator:
Weighted average number of shares out-standing used to calculate basic income per share (in Shares)	23,559	23,185	22,354
Basic income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 5,190.00	$ 4,080.00	$ 3,090.00
Basic distributed income per share applicable to common stockholders (in Dollars per share)	$ (610)	$ (390)	$ (470)
Basic undistributed income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 4,580	$ 3,690	$ 2,620
Numerator:
Distributed income applicable to common stockholders	14,367,000	9,061,000	10,497,000
Diluted distributed income applicable to common stockholders	14,367,000	9,061,000	10,497,000
Undistributed income from continuing operations applicable to common stockholders	107,879,000	85,471,000	58,572,000
Diluted undistributed income from continuing operations applicable to common stockholders	107,879,000	85,471,000	58,572,000
Denominator:
Weighted average number of shares outstanding used to calculate basic income per share (in Shares)	23,559	23,185	22,354
Weighted average number of shares from stock options (in Shares)	261	386	474
Conversion of Class B to Class A (in Shares)	2,562	2,620	3,342
Weighted average number of shares outstanding used to calculate diluted income per share (in Shares)	26,382	26,191	26,170
Diluted income from continuing operations per share available to common stockholders	5,140	4,020	3,030
Diluted distributed income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ (610)	$ (390)	$ (470)
Diluted undistributed income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 4,530	$ 3,630	$ 2,560
Common Class B [Member] \| Basic [Member]
Numerator:
Distributed income applicable to common stockholders	(1,562,000)	(1,024,000)	(1,569,000)
Numerator:
Distributed income applicable to common stockholders	1,562,000	1,024,000	1,569,000
Diluted distributed income applicable to common stockholders	1,562,000	1,024,000	1,569,000
Common Class B [Member] \| Distributed [Member]
Numerator:
Reallocation of distributed income as a result of conversion of dilutive stock options	(15,000)	(15,000)	(28,000)
Reallocation of undistributed income as a result of conversion of dilutive stock options	(15,000)	(15,000)	(28,000)
Common Class B [Member] \| Diluted [Member]
Numerator:
Distributed income applicable to common stockholders	(1,547,000)	(1,009,000)	(1,541,000)
Numerator:
Distributed income applicable to common stockholders	1,547,000	1,009,000	1,541,000
Diluted distributed income applicable to common stockholders	1,547,000	1,009,000	1,541,000
Undistributed income from continuing operations applicable to common stockholders	11,616,000	9,516,000	8,598,000
Diluted undistributed income from continuing operations applicable to common stockholders	11,616,000	9,516,000	8,598,000
Common Class B [Member] \| Undistributed [Member]
Numerator:
Reallocation of distributed income as a result of conversion of dilutive stock options	(116,000)	(142,000)	(159,000)
Reallocation of undistributed income as a result of conversion of dilutive stock options	(116,000)	(142,000)	(159,000)
Common Class B [Member]
Numerator:
Income from continuing operations applicable to common stockholders	13,294,000	10,682,000	10,326,000
Distributed income applicable to common stockholders	(1,562,000)	(1,024,000)	(1,569,000)
Basic undistributed income from continuing operations applicable to common stockholders	11,732,000	9,658,000	8,757,000
Denominator:
Weighted average number of shares out-standing used to calculate basic income per share (in Shares)	2,562	2,620	3,342
Basic income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 5,190.00	$ 4,080.00	$ 3,090.00
Basic distributed income per share applicable to common stockholders (in Dollars per share)	$ (61,000)	$ (390)	$ (470)
Basic undistributed income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 4,580	$ 3,690	$ 2,620
Numerator:
Distributed income applicable to common stockholders	1,562,000	1,024,000	1,569,000
Diluted distributed income applicable to common stockholders	1,562,000	1,024,000	1,569,000
Undistributed income from continuing operations applicable to common stockholders	11,732,000	9,658,000	8,757,000
Diluted undistributed income from continuing operations applicable to common stockholders	11,732,000	9,658,000	8,757,000
Denominator:
Weighted average number of shares outstanding used to calculate basic income per share (in Shares)	2,562	2,620	3,342
Weighted average number of shares outstanding used to calculate diluted income per share (in Shares)	2,562	2,620	3,342
Diluted income from continuing operations per share available to common stockholders	$ 5,140	$ 4,020	$ 3,030
Diluted distributed income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ (610)	$ (390)	$ (470)
Diluted undistributed income from continuing operations per share applicable to common stockholders (in Dollars per share)	$ 4,530	$ 3,630	$ 2,560

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of dilutive convertible securities excluding adjustments related to ESOP convertible preferred stock, stock options, and restrictive stock units.

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The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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Dividends declared in the period and the contractual amount of dividends (or interest on participating income bonds) that must be paid per security.

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The earnings attributable to each security on the basis that all of the earnings for the period had been distributed (to the extent that each security may share in earnings). This is the earnings amount which reflects the participation rights in undistributed earnings of each security.

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Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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