Note 8 - Stock Repurchase Program (Details) - Stock Repurchase Program - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Repurchase Program [Abstract]
Cumulative balance, shares repurchased	2,360	1,715	664	0
Cumulative balance, average price per share	$ 39.87	$ 36.04	$ 31.06	$ 0
Cumulative balance, total amount	$ 94,099	$ 61,813	$ 20,615	$ 0
Repurchases, shares repurchased	645	1,051	664
Repurchases, average price per share	$ 50.05	$ 39.19	$ 31.06
Repurchases, total amount	$ 32,286	$ 41,198	$ 20,615

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 29, 30, 31
-Article 5

Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration