Number of shares that have been repurchased and retired during the period.

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Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Note 9 - Share Repurchase Program (Details Textual) $ in Millions		6 Months Ended	12 Months Ended
	Jul. 07, 2017	Jun. 30, 2018 USD ($) shares	Dec. 31, 2017 shares	Aug. 15, 2017 shares	Nov. 04, 2015 USD ($) shares	Dec. 31, 2007 shares
Stock Repurchase Program, Number of Shares Authorized to be Repurchased		1,000,000		3,300,000	2,000,000	1,000,000
Stock Repurchase Program, Authorized Amount \| $		$ 16.3			$ 40.0
Stock Repurchased and Retired During Period, Shares		0	0
Stock Split from [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	5
Stock Split To [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio	3