Note 2 - Acquisitions and Dispositions - Unaudited Pro Forma Results (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
The 2016 Acquisitions [Member]
Revenue (less agency commissions)	$ 825,787	$ 701,550
Net income	$ 57,795	$ 39,360
Basic net income per share (in dollars per share)	$ 0.80	$ 0.58
Diluted net income per share (in dollars per share)	$ 0.79	$ 0.57
The 2015 Acquisitions [Member]
Revenue (less agency commissions)		$ 621,530	$ 559,538
Net income		$ 46,181	$ 59,342
Basic net income per share (in dollars per share)		$ 0.68	$ 1.03
Diluted net income per share (in dollars per share)		$ 0.67	$ 1.02
Hoak and SJL [Member]
Revenue (less agency commissions)			$ 565,251
Net income			$ 50,771
Basic net income per share (in dollars per share)			$ 0.88
Diluted net income per share (in dollars per share)			$ 0.87