Stock-based compensation and warrants (Tables)

3 Months Ended

Mar. 31, 2015

Stock-based compensation expense by award type was as follows (in thousands):

	Three months ended March 31,
		2015		2014
Stock options	$	4,755	$	2,477
Restricted stock awards		—		16
Restricted stock units		617		—
Employee stock purchase plan		60		—
	$	5,432	$	2,493

The following table summarizes the stock option activity under the Company’s equity award plans (share values in thousands):

	Shares			Weighted-average exercise price per share
Outstanding at December 31, 2014		3,652		$	12.30
Granted		776		$	96.74
Exercised		(347	)	$	7.07
Canceled or forfeited		(7	)	$	25.16
Outstanding at March 31, 2015		4,074		$	28.80
Exercisable at March 31, 2015		1,297		$	6.91
Vested and expected to vest at March 31, 2015		3,997		$	29.12

Restricted stock units

The following table summarizes the restricted stock unit activity under the Company’s equity award plans (share values in thousands):

	Shares		Weighted-average grant date fair value
Unvested balance at December 31, 2014		179	$	30.47
Granted		—		—
Vested		—		—
Forfeited		—		—
Unvested balance at March 31, 2015		179	$	30.47