Note 3 - Stock Based Compensation (Tables)

6 Months Ended

Jun. 30, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

	Three months ended June 30,				Six months ended June 30,
	2014		2013		2014		2013
Stock options and employee stock purchase plan		1,954		2,191		3,175		3,830
Restricted stock awards		92		350		153		414
Total stock-based compensation expense		2,047		2,541		3,329		4,244

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Three months ended June 30,						Six months ended June 30,
	2014			2013			2014			2013
Expected volatility		54	%		58	%		54	%		59	%
Expected life (in years)		4.2			4.0			4.2			4.0
Risk-free interest rate		1.79	%		0.73	%		1.79	%		0.74	%
Dividend yield		—	%		—	%		—	%		—	%
Fair value per stock option	$	10.77		$	6.81		$	10.77		$	6.77
Forfeiture rate		8	%		8	%		8	%		8	%

Schedule of Share-based Compensation, Activity [Table Text Block]

	Number of Options  (in thousands)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2013		9,228	$	4.45		1.61	$	186,169
Granted		991		24.75
Exercised		(238)		5.26
Forfeited		(19)		15.48
Outstanding at June 30, 2014		9,962	$	6.42		2.75	$	267,200
Exercisable at June 30, 2014		8,136	$	3.47		2.24	$	242,324

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

	Number of Shares (in thousands)		Weighted Average Grant Date Fair Value
Non-vested at December 31, 2013		16	$	15.36
Granted		72		24.74
Forfeited		—		—
Vested		(16)		15.36
Non-vested at June 30, 2014		72	$	24.74