STOCK COMPENSATION (Tables)

3 Months Ended

Mar. 31, 2013

Summary of Stock Option Activity

A summary of the Company’s stock option activity with respect to the three months ended March 31, 2013 follows:

Stock Options	Underlying Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2012		2,522,522		$	11.76
Granted		242,320			28.76
Exercised		(64,390	)		8.97
Canceled		(5,774	)		14.83
Outstanding at March 31, 2013		2,694,678		$	13.35		8.3	$	63,877,000
Vested at March 31, 2013 and expected to vest		2,502,875		$	13.24		8.3	$	59,634,000
Exercisable at March 31, 2013		656,805		$	12.36		6.8	$	16,428,000

Assumptions for Measuring Fair Values of Stock Options Granted

The fair values of stock options granted during the period presented were measured on the date of grant using the Black-Scholes-Merton option-pricing model, with the following assumptions:

	Three Months Ended March 31,
	2013			2012
Risk-free interest rate		0.7	%		1.1	%
Expected dividend yield		0	%		0	%
Expected lives		4.9 years			5.3 years
Expected volatility		80.0	%		79.7	%

Summary of Stock-Based Compensation Expense Recognized in Statements of Operations

A summary of the stock-based compensation expense, including stock options, restricted stock, RSUs, and SARs recognized in the condensed consolidated statements of operations and comprehensive loss is as follows:

	Three Months Ended
	March 31, 2013		March 31, 2012
	(in thousands)
Research and development	$	530	$	253
General and administrative		1,141		455
Total	$	1,671	$	708