Restructuring Charge (Details)		1 Months Ended		3 Months Ended		9 Months Ended
	Sep. 26, 2016 USD ($) item	Dec. 31, 2016 USD ($)	Sep. 30, 2016 shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) shares	Sep. 30, 2017 USD ($) shares	Sep. 30, 2016 USD ($)	Feb. 29, 2016 USD ($) ft²
Restructuring
Restructuring charges					$ 4,130,000	$ 386,000	$ 4,130,000
Stock compensation expense (reduction)				$ 2,600,000	4,400,000	8,300,000	16,000,000
Construction allowance		$ 5,914,000		5,325,000		5,325,000
Restructuring Reserve
Initial charge related to employee benefits, Beginning Balance						1,751,000
Payments for the period						(1,738,000)
Balance at the End of the year		$ 1,751,000		$ 13,000		13,000
Workforce reduction
Restructuring
Approximate positions to be eliminated (as a percent)	17.00%
Approximate positions to be eliminated | item	65
Approximate current positions to be eliminated | item	60
Restructuring charges					4,100,000		4,100,000
One-time termination benefit					2,500,000		2,500,000
Benefit plan severance cost					$ 593,000		$ 593,000
Granted (in shares) | shares			731,000
Vesting period			3 years
930 Winter Street, Walham, MA
Restructuring
Area of space leased | ft²								10,281
Construction allowance								$ 617,000
930 Winter Street, Walham, MA | Lease
Restructuring
Area of space leased | ft²								10,281
Estimated period to sub-lease			9 months
Leasehold impairment charge	$ 970,000					$ 386,000
Leasehold improvement cost	$ 193,000
Stock options
Restructuring
Forfeited (in shares) | shares						2,165
Granted (in shares) | shares						1,533
Stock options | Workforce reduction
Restructuring
Forfeited (in shares) | shares					762,000
Stock compensation expense (reduction)					$ (837,000)