In June 2003, Vertex adopted a plan to restructure its operations to coincide with its increasing internal emphasis on advancing drug candidates through clinical development to commercialization. The restructuring was designed to re-balance the Company's relative investments in research and development to better support the Company's long-term strategy. At that time, the restructuring plan included a workforce reduction, write-offs of certain assets and a decision not to occupy approximately 290,000 square feet of specialized laboratory and office space in Cambridge, Massachusetts under lease to Vertex (the "Kendall Square Lease"). The Kendall Square Lease commenced in January 2003 and has a 15-year term. In the second quarter of 2005, the Company revised its assessment of its real estate requirements and decided to use approximately 120,000 square feet of the facility subject to the Kendall Square Lease (the "Kendall Square Facility") for its operations, beginning in 2006. The remaining rentable square footage of the Kendall Square Facility currently is subleased to third parties.

The restructuring expense incurred in the three and nine months ended September 30, 2012 and 2011 relates only to the portion of the Kendall Square Facility that the Company is not occupying and does not intend to occupy for its operations. The remaining lease obligations, which are associated with the portion of the Kendall Square Facility that the Company occupies and uses for its operations, are recorded as rental expense in the period incurred.

In estimating the expense and liability under its Kendall Square Lease obligation, the Company estimated (i) the costs to be incurred to satisfy rental and build-out commitments under the lease (including operating costs), (ii) the lead-time necessary to sublease the space, (iii) the projected sublease rental rates and (iv) the anticipated durations of subleases. The Company uses a credit-adjusted risk-free rate of approximately 10% to discount the estimated cash flows. The Company reviews its estimates and assumptions on at least a quarterly basis, and intends to continue such reviews until the termination of the Kendall Square Lease, and will make whatever modifications the Company believes necessary, based on the Company's best judgment, to reflect any changed circumstances. The Company's estimates have changed in the past, and may change in the future, resulting in additional adjustments to the estimate of the liability. Changes to the Company's estimate of the liability are recorded as additional restructuring expense (credit). In addition, because the Company's estimate of the liability includes the application of a discount rate to reflect the time-value of money, the Company records imputed interest costs related to the liability each quarter. These costs are included in restructuring expense (credit) on the Company's condensed consolidated statements of operations.

In each period, the Company records lease restructuring expense attributable to imputed interest related to the restructuring liability. In certain periods, the restructuring expense also reflects the revision of certain key estimates and assumptions about building operating expenses and sublease income. The activities related to the restructuring liability for the three and nine months ended September 30, 2012 and 2011 were as follows:

	Three Months Ended September 30,						Nine Months Ended September 30,

	2012			2011			2012			2011
	(in thousands)
Liability, beginning of the period	$	24,830		$	28,205		$	26,313		$	29,595
Cash payments		(3,726	)		(3,685	)		(11,137	)		(11,158	)
Cash received from subleases		2,355			2,483			7,329			7,065
Restructuring expense (credit)		696			(419	)		1,650			1,082

Liability, end of the period	$	24,155		$	26,584		$	24,155		$	26,584