Note 6 - Fair Value Measurements - Summary of Activity for Metro Bonds (Details) - Metropolitan District Bond Securities [Member] - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Balance at beginning of period	$ 30,162	$ 25,911
Increase in fair value (recorded in other comprehensive income)	382	950
Change due to accretion of principal	460	416
Cash receipts
Balance at end of period	$ 31,004	$ 27,277

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

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