Note 13 - Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other expense		$ 3,718	$ 3,249	$ 12,158	$ 11,407
Tax expense		(1,910)	(5,291)	(9,349)	(17,320)
Net of tax		17,333	10,179	42,668	35,164
Other expense		(3,718)	(3,249)	(12,158)	(11,407)
Total before tax		19,243	15,470	52,017	52,484
Total income tax provision		1,910	5,291	9,349	17,320
Reclassification out of Accumulated Other Comprehensive Income [Member]
Tax expense		(38)	59	(116)	178
Net of tax		(84)	(81)	(252)	(242)
Total before tax		(122)		(368)
Total income tax provision		38	(59)	116	(178)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swap [Member]
Net of tax		80		(161)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Tax expense			78		78
Net of tax			(108)		(108)
Total income tax provision			(78)		(78)
Net loss on sale of securities			(186)		(186)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] | Interest Rate Swap [Member]
Other expense		116		(235)
Tax expense		(36)		(74)
Other expense		(116)		235
Total income tax provision		36		74
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Other expense	[1]	132	152	396	454
Other expense	[1]	(132)	(152)	(396)	(454)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Other expense	[1]	10	(12)	28	(34)
Other expense	[1]	$ (10)	12	$ (28)	34
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Total before tax			$ (140)		$ (420)

[1] These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (See Note 9 of the Notes to Consolidated Financial Statements "Pension and Other Postretirement Benefit Plans".)