Note 13 - Stockholders' Equity (Details) - Amounts Reclassified Out of Accumulated Other Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total income tax provision	$ 6,988	$ 7,060	$ 7,598	$ 6,927	$ 6,458	$ 6,024	$ 6,155	$ 4,319	$ 28,573		$ 22,956		$ 21,847
Net of tax	11,057	11,201	11,685	10,296	11,948	9,421	9,627	6,756	44,239		37,752		34,331
OTTI charges											1,419		776
Tax expense	18,045	18,261	19,283	17,223	18,406	15,445	15,782	11,075	72,812		60,708		56,178
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains (losses) on available for sale securities									2,875		3,021
Total income tax provision									(1,241)		(1,321)
Net of tax									1,634		1,700
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member] | Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense									(700)	[1]	(1,237)	[1]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member] | Prior Service Credits [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense									45	[1]	46	[1]
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total income tax provision									311		521
Net of tax									(344)		(670)
Tax expense									(655)		(1,191)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Other-than-Temporary Impairment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total income tax provision											621
Net of tax											(798)
OTTI charges											$ (1,419)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 12 of the Notes to Consolidated Financial Statements "Pension and Other Postretirement Benefit Plans").