Note 11 - Stockholders' Equity and Stock Incentive Plans (Details Textual) - USD ($) $ in Thousands			3 Months Ended			12 Months Ended
		May 17, 2012	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 12, 2018	May 16, 2012
Stock Repurchased and Retired During Period, Shares	[1],[2]					1,087,000	1,853,000	1,198,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value						$ 4,700	$ 7,800	$ 3,900
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value						600	$ 1,200	$ 1,600
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total						0
Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total						$ 15,700
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition						2 years 6 months
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period						3 years
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total						$ 8,500
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition						2 years 8 months 12 days
Share Based Compensation Arrangement By Share Based Payment Award, Evaluation of Performance Conditions Period						3 years
Share Based Compensation Arrangement By Share Based Payment Award, Awards if Only Threshhold Performance Met, Percentage						50.00%
Share Based Compensation Arrangement By Share Based Payment Award, Awards for Target Performance, Percentage						100.00%
Share Based Compensation Arrangement By Share Based Payment Award, Awards for Maximum Performance, Percentage						200.00%
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period			395,964	486,805	268,429
Shares Issued Per Unit			1.67	1.57	0.80
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation			125,004	149,268	94,776
Share Based Payment Arrangement, Shares Issued In Period, Net of Tax Withholdings			270,960	337,537	173,653
Shares to be Issued to Settle PSUs						1,400,000
Career Shares [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total						$ 1,200
Career Shares [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award, Award Eligibility Minimum Age						55 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period						10 years
Career Shares [Member] | Executive Officer [Member] | Share-based Payment Arrangement, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award, Service Period						10 years
Career Shares [Member] | Executive Officer [Member] | Share-based Payment Arrangement, Tranche Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award, Service Period						15 years
Career Shares [Member] | Executive Officer [Member] | Share-based Payment Arrangement, Tranche Three [Member]
Share Based Compensation Arrangement By Share Based Payment Award, Service Period						20 years
Stock Incentive Plan 2012 [Member] | Share-based Payment Arrangement, Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award Expiration of Plan		10 years
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized		4,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized		21,000,000								17,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant						3,300,000
Share Based Compensation Arrangement By Share Based Payment Award, Number of Authorized and Unissued, Shares						7,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period						3 years
The 2018 Plan [Member]
Stock Repurchase Program, Authorized Amount									$ 100,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount						$ 72,500

[1] All shares repurchased have been retired and constitute authorized but unissued shares.

[2] Shares repurchased reflect repurchases settled during the twelve months ended December 31, 2019, 2018 and 2017. These amounts exclude repurchases, if any, traded but not yet settled on or before December 31, 2019, 2018 and 2017.