Note 9 - Dividends and Dividend Equivalents (Details) - Cash Dividends - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014
2015:
Dividend Declared per Share	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.15	$ 0.15	$ 0.15
Total Amount	$ 7,938	$ 7,901	$ 7,925	$ 7,854	$ 5,826	$ 5,823	$ 5,817

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

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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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration