Note 9 - Stock-based Compensation (Details Textual) - USD ($)	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 10,903	$ 100,815
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	10,200,000
Allocated Share-based Compensation Expense	$ 5,386,000	$ 4,240,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 40 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 5.45
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	677	9,975
Proceeds from Stock Options Exercised	$ 2,000	$ 26,000
Employee Stock Option [Member]
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	400,000	10,000
Allocated Share-based Compensation Expense	2,100,000	2,000,000
Proceeds from Stock Options Exercised	1,836	26,425
Restricted Stock Units (RSUs) [Member]
Allocated Share-based Compensation Expense	$ 3,300,000	$ 2,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	761,178
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 10,400,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 40 days

Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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

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