Note 6 - Stock-Based Compensation (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Stock Options [Abstract]
Shares	1,183,000	1,520,484			2,332,904	2,332,904
Weighted-average exercise price	$ 30.37	$ 30.62			$ 32.34	$ 32.34
Weighted-average remaining contractual life	1 year 73 days	1 year 6 months	1 year 219 days			1 year 73 days
Aggregate intrinsic value	$ 3,148	$ 5,010	$ 3,156	$ 3,148		$ 1,388
Exercisable, September 30, 2015	1,098,400			1,098,400
Exercisable, September 30, 2015	$ 30.79			$ 30.79
Exercisable, September 30, 2015	1 year 73 days
Exercisable, September 30, 2015	$ 3,148			$ 3,148
Shares, exercised	(74,000)	(69,600)	(3,750)	(147,350)	0
Weighted-average exercise price, exercised	$ 23.37	$ 23.37	$ 23.37
Shares, forfeited	(10,600)	(267,884)	(808,670)
Weighted-average exercise price, forfeited	$ 36.56	$ 33.99	$ 35.63
Shares	1,098,400	1,183,000	1,520,484	1,098,400
Weighted-average exercise price	$ 30.79	$ 30.37	$ 30.62	$ 30.79

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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