Note 6 - Fair Value Measurements - Summary of Activity for Metro Bonds (Details) - Metropolitan District Bond Securities [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Balance at beginning of period	$ 31,004	$ 27,277	$ 30,162	$ 25,911
Increase in fair value (recorded in other comprehensive income)	398	915	780	1,865
Change due to accretion of principal	462	412	922	828
Cash receipts
Balance at end of period	$ 31,864	$ 28,604	$ 31,864	$ 28,604

The fair value as of the balance sheet date of firm holdings in fixed income obligations issued by state and local governments and authorities. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

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