Note 12 - Stockholders' Equity and Earnings Per Share - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance	$ 1,828,539	$ 1,747,778	$ 1,602,888
Total other comprehensive (loss)/income, net of tax	1,204	4,711	(2,857)
Balance	1,973,304	1,828,539	1,747,778
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Net unrealized (losses)/gains arising during the period, pre-tax	1,843	11,603
Reclassification adjustment for net losses/(gains) included in net income, pre-tax	(1,006)	(4,898)
Total other comprehensive (loss)/income, pre-tax	837	6,705
Net unrealized (losses)/gains arising during the period, tax	775	4,878
Reclassification adjustment for net losses/(gains) included in net income, tax	(423)	(2,059)
Total other comprehensive (loss)/income, tax	352	2,819
Balance	(1,545)	(5,431)
Net unrealized (losses)/gains arising during the period, net of tax	1,068	6,725
Reclassification adjustment for net losses/(gains) included in net income, net of tax	(583)	(2,839)
Total other comprehensive (loss)/income, net of tax	485	3,886
Balance	(1,060)	(1,545)	(5,431)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Net unrealized (losses)/gains arising during the period, pre-tax	1,241	1,423
Reclassification adjustment for net losses/(gains) included in net income, pre-tax
Total other comprehensive (loss)/income, pre-tax	1,241	1,423
Net unrealized (losses)/gains arising during the period, tax	522	598
Reclassification adjustment for net losses/(gains) included in net income, tax
Total other comprehensive (loss)/income, tax	522	598
Balance	(2,170)	(2,995)
Net unrealized (losses)/gains arising during the period, net of tax	719	825
Reclassification adjustment for net losses/(gains) included in net income, net of tax
Total other comprehensive (loss)/income, net of tax	719	825
Balance	(1,451)	(2,170)	(2,995)
AOCI Attributable to Parent [Member]
Net unrealized (losses)/gains arising during the period, pre-tax	3,084	13,026
Reclassification adjustment for net losses/(gains) included in net income, pre-tax	(1,006)	(4,898)
Total other comprehensive (loss)/income, pre-tax	2,078	8,128
Net unrealized (losses)/gains arising during the period, tax	1,297	5,476
Reclassification adjustment for net losses/(gains) included in net income, tax	(423)	(2,059)
Total other comprehensive (loss)/income, tax	874	3,417
Balance	(3,715)	(8,426)	(5,569)
Net unrealized (losses)/gains arising during the period, net of tax	1,787	7,550
Reclassification adjustment for net losses/(gains) included in net income, net of tax	(583)	(2,839)
Total other comprehensive (loss)/income, net of tax	1,204	4,711	(2,857)
Balance	$ (2,511)	$ (3,715)	$ (8,426)