SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2013

Accounting Policies [Abstract]

Summary of Estimated Useful Lives of Property and Equipment

The Company generally depreciates the cost of its property and equipment using the straight-line method over the estimated useful lives of the respective assets, which are summarized as follows:

Asset Category	Useful lives
Lab equipment	5 years
Office equipment	5 years
Leasehold improvements	Lesser of the useful life or the term of the respective lease
Building	30 years
Construction in Progress	Not depreciated until put into service

Amounts Included in Property and Equipment

Amounts included in property and equipment are as follows:

	As of December 31,
	2013			2012
	(in thousands)
Lab equipment	$	7,728		$	6,890
Office equipment		1,432			1,301
Leasehold improvements		10,058			10,058
Building		1,856			1,856
Construction in progress		11,303			—
Property and equipment, gross		32,377			20,105
Less accumulated depreciation		(17,328	)		(16,708	)
Property and equipment, net	$	15,049		$	3,397

Assets and Liabilities Measured at Fair Value on Recurring Basis

The Company’s assets and liabilities measured at fair value on a recurring basis consisted of the following as of the date indicated:

	Fair Value Measurement as of December 31, 2013
	Total		Level 1		Level 2		Level 3
	(in thousands)
Restricted investments, current	$	7,250	$	7,250		$—		$—
Restricted investments, noncurrent		647		647
Total assets	$	7,897	$	7,897		$—		$—

	Fair Value Measurement as of December 31, 2013
	Total		Level 1		Level 2		Level 3
	(in thousands)
Warrants*	$	9,006		$—		$—	$	9,006
Total liabilities	$	9,006		$—		$—	$	9,006

	Fair Value Measurement as of December 31, 2012
	Total		Level 1		Level 2		Level 3
	(in thousands)
Warrants*	$	65,193		$—		$—	$	65,193
Total liabilities	$	65,193		$—		$—	$	65,193

*See “Note 8—Warrants” for additional information related to the determination of fair value of the warrants.