Note 8 - Stockholders' Equity (Deficiency) (Details Textual) $ / shares in Units, $ in Thousands					12 Months Ended
	Jan. 01, 2017 shares	Jan. 01, 2016 shares	Jun. 30, 2015 shares	Nov. 14, 2013 shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares	Dec. 31, 2013 shares
Common Stock, Shares Authorized					200,000,000	200,000,000
Common Stock, Par or Stated Value Per Share | $ / shares					$ 0.001	$ 0.001
Common Stock, Number of Voting Rights					1
Common Stock, Capital Shares Reserved for Future Issuance, Annual Increase, Maximum		1,042,766
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | $ / shares					$ 16.87	$ 28.637	$ 14.087
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | $					$ 9,418	$ 27,885	$ 4,800
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $					$ 3,380	$ 11,779
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition					1 year 282 days	2 years 151 days
Subsequent Event [Member]
Common Stock, Capital Shares Reserved for Future Issuance, Annual Increase, Maximum	1,072,870
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, Number of Shares Available for Grant					0
The 2005 Stock Plan [Member] | Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period								4 years
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%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			500,000
Percent of Shares Increase, Employee Stock Purchase Plan			1.00%
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		21,383
2015 ESPP [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	158,695