Note 14 - Stockholders' Equity - Dividends Declared (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016
Dividends Per Share of Common Stock (in dollars per share)	$ 0.64	$ 0.64	$ 0.56	$ 0.56	$ 0.56	$ 0.56	$ 0.50	$ 0.50
Record Date	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016
Total $ Amount	$ 24,443	$ 24,566	$ 21,799	$ 21,902	$ 21,853	$ 21,951	$ 19,709	$ 19,852
Payment Date	Sep. 18, 2018	Jun. 19, 2018	Mar. 20, 2018	Dec. 19, 2017	Sep. 19, 2017	Jun. 20, 2017	Mar. 21, 2017	Dec. 20, 2016

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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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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