Note 7 - Stockholders' Equity and Stock-based Compensation Expense - Activity Under the 2004 Equity Incentive Plan (Details)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Balance, shares available for grant (in shares)	721,657
Balance, stock options outstanding (in shares)	1,116,472
Balance, weighted-average exercise price (in dollars per share) | $ / shares	$ 9.56
Additional shares reserved (in shares)	1,600,000
Options granted, shares available for grant (in shares)	(154,000)
Options granted, stock options outstanding (in shares)	154,000
Options granted, weighted-average exercise price (in dollars per share) | $ / shares	$ 21.82
Stock awards granted(1) (2) (in shares)	(558,694)	[1],[2]
Options exercised, stock options outstanding (in shares)	(447,673)
Options exercised, weighted-average exercise price (in dollars per share) | $ / shares	$ 8.90
Options canceled, shares available for grant (in shares)	53,393
Options canceled, stock options outstanding (in shares)	(53,393)
Options canceled, weighted-average exercise price (in dollars per share) | $ / shares	$ 16.58
Stock awards canceled(1) (in shares)	110,278	[2]
Balance, shares available for grant (in shares)	1,772,634
Balance, stock options outstanding (in shares)	769,406
Balance, weighted-average exercise price (in dollars per share) | $ / shares	$ 11.91

[1] Included in 'Stock awards granted' of 558,694, was 221,540 fungible shares relating to 104,500 of PSUs granted. These PSUs may result in a lower number of shares of common stock that may be released on January 1, 2018, based on PSUs forfeited due to employment terminations and the degree of achievement of two performance goals compared to 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 Amended and Restated 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.