Note 4 - Stockholders' Equity (Details Textual) - USD ($) $ in Thousands						3 Months Ended		12 Months Ended	51 Months Ended
	Jan. 01, 2018	Jan. 01, 2017	Jan. 01, 2016	Jun. 30, 2015	Nov. 14, 2013	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2013	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross
Common Stock, Capital Shares Reserved for Future Issuance, Annual Increase, Maximum	1,125,846	1,072,870	1,042,766
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value						$ 7,824
Restricted Stock Units and Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount						3,932,450	4,339,384
Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total						$ 1,366			$ 1,366
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition						286 days
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total						$ 93,961			$ 93,961
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition						3 years 46 days
The 2005 Stock Plan [Member]
Common Stock, Capital Shares Reserved for Future Issuance								4,713,319
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period								4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross									0
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant						0			0
The 2013 Omnibus Equity Award Plan [Member]
Common Stock, Capital Shares Reserved for Future Issuance					1,904,633
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Reserved for Grant					4.00%
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Maximum					5.00%
The 2013 Omnibus Equity Award Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					4 years
2015 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate				15.00%
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent				85.00%
Percent of Shares Increase, Employee Stock Purchase Plan				1.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				500,000
Common Stock Availability Threshold, Employee Stock Purchase Plan				2.00%
Shares Increase Threshold, Employee Stock Purchase Plan				400,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	188,813	158,695	21,383