Note 13 - Stockholders' Equity - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 19, 2017	May 05, 2017	Feb. 06, 2017	Nov. 10, 2016	Aug. 05, 2016	May 06, 2016	Feb. 05, 2016	Nov. 06, 2015	Aug. 10, 2015
Dividends Per Share of Common Stock (in dollars per share)		$ 0.56	$ 0.50	$ 0.50	$ 0.50	$ 0.50	$ 0.44	$ 0.44	$ 0.44
Record Date		May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	May 31, 2016	Nov. 30, 2015	Aug. 31, 2015
Total $ Amount	$ 22,000	$ 21,951	$ 19,709	$ 19,852	$ 20,019	$ 20,171	$ 18,044	$ 18,208	$ 18,179
Payment Date		Jun. 20, 2017	Mar. 21, 2017	Dec. 20, 2016	Sep. 20, 2016	Jun. 21, 2016	Mar. 15, 2016	Dec. 15, 2015	Sep. 15, 2015

Date the declared dividend will be paid, in CCYY-MM-DD format.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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Amount of paid and unpaid cash dividends declared for classes of stock, for example, but not limited to, common and preferred.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957935&loc=d3e64057-112817

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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