Note 10 - Stock Based Compensation - Summary of Unvested Stock Options, Restricted Stock and Performance Shares (Details)	3 Months Ended
Mar. 31, 2018 $ / shares shares
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested Stock Options, beginning balance \| shares	757,269
Vested during period, unvested stock options \| shares	(21,510)
Forfeited, unvested stock options \| shares	(5,311)
Unvested Stock Options, ending balance \| shares	730,448
Unvested Stock Options, beginning balance, weighted average grant date fair value \| $ / shares	$ 15.20
Vested during period, weighted average grant date fair value \| $ / shares	13.99
Forfeited, weighted average grant date fair value \| $ / shares	13.90
Unvested Stock Options, ending balance, weighted average grant date fair value \| $ / shares	$ 15.25
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested equity awards other than options, beginning balance \| shares	265
Unvested equity awards other than options, ending balance \| shares	265
Unvested equity awards other than options, beginning balance, weighted average grant date fair value \| $ / shares	$ 44.23
Unvested equity awards other than options, ending balance, weighted average grant date fair value \| $ / shares	$ 44.23
Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested equity awards other than options, beginning balance \| shares	276,250
Forfeited, equity awards other than options \| shares	(17,250)
Unvested equity awards other than options, ending balance \| shares	259,000
Unvested equity awards other than options, beginning balance, weighted average grant date fair value \| $ / shares	$ 42.08
Forfeited, equity awards other than options, weighted average grant date fair value \| $ / shares	40.65
Unvested equity awards other than options, ending balance, weighted average grant date fair value \| $ / shares	$ 42.17

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Number of non-vested options outstanding.

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Number of non-vested options forfeited.

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- Definition

Weighted average grant-date fair value of non-vested options forfeited.

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- Definition

Weighted average grant-date fair value of non-vested options outstanding.

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- Definition

Number of options vested.

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Weighted average grant-date fair value of options vested.

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