Note 5 - Accumulated Other Comprehensive Income - Changes in AOCI (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Beginning balance 1		$ 1,407,287
Ending balance		1,432,493
AOCI Attributable to Parent [Member]
Beginning balance 1	[1]	3,992	$ 22,071
Adoption of accounting standards (Note 2)	[1]	(3,992)
Other comprehensive income before reclassifications	[1]		2,271
Amounts reclassified from AOCI	[1],[2]		(285)
Ending balance	[1]		$ 24,057

[1] All amounts net-of-tax.

[2] See separate table below for details about these reclassifications.