Restructuring Charge (Details)		1 Months Ended	3 Months Ended		6 Months Ended
	Sep. 26, 2016 USD ($) item shares	Sep. 30, 2016 shares	Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Feb. 29, 2016 USD ($) ft²
Restructuring
Restructuring charges			$ 386,000
Stock compensation expense (reduction)			2,600,000	$ 7,200,000
Construction allowance			5,718,000		$ 5,914,000
Restructuring Reserve
Initial charge related to employee benefits, Beginning Balance			1,751,000
Payments for the period			(1,287,000)
Balance at the End of the year			464,000		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		847,000
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			1,176
Granted (in shares) | shares			1,187
Stock options | Workforce reduction
Restructuring
Forfeited (in shares) | shares	762,000
Stock compensation expense (reduction)	$ 837,000