Note 6 - Investments in Marketable Securities (Details Textual) - USD ($)	Dec. 31, 2017	Sep. 30, 2017
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	$ 181,540,000	$ 165,872,000
Deferred Tax Liabilities, Investments	$ 48,140,000	$ 64,550,000

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant