Note 3 - Impact of Recently Issued Accounting Pronouncements (Details Textual) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
Unrecognized Excess Tax Benefits							$ 0
Income Tax Expense (Benefit)						$ 38,061	$ 40,214	$ 32,389
Accounting Standards Update 2016-09 [Member]
Income Tax Expense (Benefit)	$ (122)	$ (735)	$ (1,725)	$ (2,654)		$ (5,236)
Effective Income Tax Rate Reconciliation, Percent						(3.70%)
Reclassification from Financing Activities to Operating Activities [Member] | Twelve Months Ended December 31, 2016 [Member]
Prior Period Reclassification Adjustment						$ 10,278
Reclassification from Financing Activities to Operating Activities [Member] | Twelve Months Ended December 31, 2015 [Member]
Prior Period Reclassification Adjustment						$ 1,445
Accounting Standards Update 2014-09 [Member] | Minimum [Member] | Scenario, Forecast [Member]
Stockholders' Equity, Period Increase (Decrease)					$ 12
Accounting Standards Update 2014-09 [Member] | Minimum [Member] | Subsequent Event [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption									$ 45
Accounting Standards Update 2014-09 [Member] | Maximum [Member] | Scenario, Forecast [Member]
Stockholders' Equity, Period Increase (Decrease)					$ 15
Accounting Standards Update 2014-09 [Member] | Maximum [Member] | Subsequent Event [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption									$ 55