Note 8 - Goodwill and Intangible Assets - Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Balance	$ 721,523	$ 704,640
Acquisitions of businesses, net	46,788	5,271
Foreign currency translation	(3,656)	11,612
Balance	764,655	721,523
Goodwill, gross			$ 1,272,459	$ 1,229,327
Accumulated impairment			(507,804)	(507,804)
Goodwill	721,523	704,640	764,655	721,523
Domestic [Member]
Balance	621,451	621,451
Acquisitions of businesses, net
Foreign currency translation
Balance	621,451	621,451
Goodwill, gross			1,124,644	1,124,644
Accumulated impairment			(503,193)	(503,193)
Goodwill	621,451	621,451	621,451	621,451
International [Member]
Balance	100,072	83,189
Acquisitions of businesses, net	46,788	5,271
Foreign currency translation	(3,656)	11,612
Balance	143,204	100,072
Goodwill, gross			147,815	104,683
Accumulated impairment			(4,611)	(4,611)
Goodwill	$ 100,072	$ 83,189	$ 143,204	$ 100,072