Note 2 - Acquisitions and Divestitures - Business Acquisition Income Statement Supplemental Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total revenues, pro forma										$ 3,293,658	$ 3,262,273
Net income	$ 24,296	$ 39,405	$ 48,484	$ 45,451	$ 22,867	$ 11,837	$ 38,945	$ 41,399	$ 157,636	115,048	189,390
Net income from continuing operations, net of tax, pro forma										$ 131,290	$ 172,462
Basic net income per share (in dollars per share)	$ 0.21	$ 0.35	$ 0.43	$ 0.40	$ 0.21	$ 0.10	$ 0.34	$ 0.36	$ 1.39	$ 1.01	$ 1.65
Basic net income per share, pro forma (in dollars per share)										1.15	1.50
Diluted net income per share (in dollars per share)	$ 0.20	$ 0.35	$ 0.43	$ 0.40	$ 0.20	$ 0.10	$ 0.34	$ 0.36	$ 1.38	1.00	1.64
Diluted net income per share, pro forma (in dollars per share)										$ 1.14	$ 1.49
Parent Company [Member]
Total revenues										$ 2,626,730	$ 2,400,819
Net income										$ 114,701	$ 167,998
Basic net income per share (in dollars per share)										$ 1.01	$ 1.46
Diluted net income per share (in dollars per share)										$ 1.00	$ 1.45
Subsidiaries [Member]
Total revenues										$ 666,928	$ 861,454
Net income										$ 16,589	$ 4,464