Note 8 - Net Income Per Share of Class A and Class B Common Stock - Earnings Per Share Reconciliation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Common Class A [Member] \| Employee Stock Option [Member]
Shares issuable pursuant to stock options not included since they were antidilutive (in shares)		18		17
Common Class A [Member] \| Distributed [Member]
Effect of dilutive stock options on net income	$ 1	$ 3	$ 5	$ 11
Conversion of Class B to Class A common shares outstanding	439	509	1,365	1,425
Common Class A [Member] \| Undistributed [Member]
Effect of dilutive stock options on net income	13	27	42	86
Conversion of Class B to Class A common shares outstanding	3,326	3,690	9,794	11,653
Common Class A [Member]
Net income applicable to common stockholders - basic	50,262	39,162	134,533	122,092
Net income applicable to common stockholders - diluted	$ 54,041	$ 43,391	$ 145,739	$ 135,267
Shares used in basic per share calculations (in shares)	23,432	23,727	23,530	23,742
Conversion of Class B common shares into Class A common shares (in shares)	1,762	2,562	1,960	2,562
Effect of dilutive stock options on weighted average common shares (in shares)	96	191	108	196
Shares used in diluted per share calculations (in shares)	25,290	26,480	25,598	26,500
Basic net income per Class A and Class B share (in dollars per share)	$ 2.14	$ 1.65	$ 5.72	$ 5.14
Diluted net income per Class A and Class B share (in dollars per share)	$ 2.14	$ 1.64	$ 5.69	$ 5.10
Common Class B [Member] \| Employee Stock Option [Member]
Shares issuable pursuant to stock options not included since they were antidilutive (in shares)
Common Class B [Member] \| Distributed [Member]
Effect of dilutive stock options on net income	$ (1)	$ (3)	$ (5)	$ (11)
Conversion of Class B to Class A common shares outstanding
Common Class B [Member] \| Undistributed [Member]
Effect of dilutive stock options on net income	(13)	(27)	(42)	(86)
Conversion of Class B to Class A common shares outstanding
Common Class B [Member]
Net income applicable to common stockholders - basic	3,779	4,229	11,206	13,175
Net income applicable to common stockholders - diluted	$ 3,765	$ 4,199	$ 11,159	$ 13,078
Shares used in basic per share calculations (in shares)	1,762	2,562	1,960	2,562
Conversion of Class B common shares into Class A common shares (in shares)
Effect of dilutive stock options on weighted average common shares (in shares)
Shares used in diluted per share calculations (in shares)	1,762	2,562	1,960	2,562
Basic net income per Class A and Class B share (in dollars per share)	$ 2.14	$ 1.65	$ 5.72	$ 5.14
Diluted net income per Class A and Class B share (in dollars per share)	$ 2.14	$ 1.64	$ 5.69	$ 5.10
Shares used in basic per share calculations (in shares)	25,194	26,289	25,490	26,304
Shares used in diluted per share calculations (in shares)	25,290	26,480	25,598	26,500
Basic net income per Class A and Class B share (in dollars per share)	$ 2.15	$ 1.65	$ 5.72	$ 5.14
Diluted net income per Class A and Class B share (in dollars per share)	$ 2.14	$ 1.64	$ 5.69	$ 5.10

Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of stock options or restrictive stock units (RSUs).

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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 amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Net Income or Loss Available to Common Stockholders plus adjustments resulting from the assumption that dilutive convertible securities were converted, options or warrants were exercised, or that other shares were issued upon the satisfaction of certain conditions.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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