Note 7 - Stockholders' Equity and Stock-based Compensation Expense (Details Textual) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Feb. 13, 2017	Dec. 31, 2016	Feb. 08, 2016
Share Based Compensation Arrangement By Share Based Payment Award Shares Available For Grant In Period Gross	[1],[2]	449,440
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized		$ 5.9
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		1 year 292 days
Modified Stock Buyback Program [Member]
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 7.2	$ 5.0	$ 5.1	$ 10.0
Stock Repurchased During Period, Shares		140,400
Treasury Stock, Value, Acquired, Cost Method		$ 2.9
Two Thousand Four Equity Incentive Plan [Member]
Number of Stock Awards Counted for Every Share Granted or Canceled		2.12
Share Based Compensation Arrangement By Share Based Payment Award Shares Available For Grant In Period Gross		449,440
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period		316,203
Two Thousand Four Equity Incentive Plan [Member] | Fungible Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award Shares Available For Grant In Period Gross		221,540
Two Thousand Four Equity Incentive Plan [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		104,500

[1] Included in 'Stock awards granted' of 449,440, was 221,540 fungible shares relating to 104,500 of PSUs granted. These PSUs mayresult in a lower number of shares of common stock that may be released on January 1, 2018, based on the achievement of two performance goals at targets that were pre-determined by the Board and disclosed in a Form 8-K on January 11, 2017.

[2] The Company has a "fungible share" provision in its 2004 Equity Incentive Plan whereby for each full-value award (RSU/PSU) issued or canceled under the Plan requires the subtraction or add back of 2.12 shares from or to the Shares Available for Grant, respectively.