Note 9 - Goodwill and Intangible Assets - Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Balance	$ 764,655	$ 721,523
Acquisitions of businesses, net	40,836	46,788
Foreign currency translation	(207)	(3,656)
Balance	805,284	764,655
Goodwill, gross			$ 1,313,088	$ 1,272,459
Accumulated impairment			(507,804)	(507,804)
Goodwill	764,655	721,523	805,284	764,655
Domestic [Member]
Balance	621,451	621,451
Acquisitions of businesses, net	37,758	0
Foreign currency translation	0	0
Balance	659,209	621,451
Goodwill, gross			1,162,402	1,124,644
Accumulated impairment			(503,193)	(503,193)
Goodwill	659,209	621,451	659,209	621,451
International [Member]
Balance	143,204	100,072
Acquisitions of businesses, net	3,078	46,788
Foreign currency translation	(207)	(3,656)
Balance	146,075	143,204
Goodwill, gross			150,686	147,815
Accumulated impairment			(4,611)	(4,611)
Goodwill	$ 146,075	$ 143,204	$ 146,075	$ 143,204