Note 7 - Stockholders' Equity and Stock-based Compensation Expense (Details Textual) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Feb. 18, 2015	Feb. 17, 2015
Modified Stock Buyback Program [Member]
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 22,300,000	$ 22,300,000	$ 40,000,000	$ 10,000,000
Stock Repurchased During Period, Shares	878,454	1,264,609
Treasury Stock, Value, Acquired, Cost Method	$ 12,500,000	$ 17,700,000
Two Thousand Four Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	286,252	934,905
Employee Stock Option [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 4.10	$ 4.10
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years 146 days
Number of Stock Awards Counted for Every Share Granted or Canceled		2.12