Restructuring Charge (Details)		1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 26, 2016 USD ($) item shares	Sep. 30, 2016 shares	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Feb. 29, 2016 USD ($) ft²
Restructuring
Restructuring charges					$ 386,000
Stock compensation expense (reduction)			$ 3,100,000	$ 4,500,000	5,700,000		$ 11,600,000
Construction allowance			5,521,000		5,521,000	$ 5,914,000
Restructuring Reserve
Initial charge related to employee benefits, Beginning Balance					1,751,000
Payments for the period					(1,573,000)
Balance at the End of the year			$ 178,000		178,000	1,751,000
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						4,400,000
One-time termination benefit						2,800,000
Benefit plan severance cost						$ 593,000
Granted (in shares) | shares		750,000
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					1,916
Granted (in shares) | shares					1,428
Stock options | Workforce reduction
Restructuring
Forfeited (in shares) | shares	762,000
Stock compensation expense (reduction)	$ 837,000