Restructuring Charge (Details)	1 Months Ended		3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) ft²	Sep. 30, 2016 USD ($) item shares	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) ft²	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) ft² shares	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) ft²	Jun. 30, 2016 USD ($) shares	Jun. 30, 2015 USD ($)
Restructuring
Restructuring charge	$ 273,000		$ 393,000	$ 386,000	$ 301,000	$ 4,130,000	$ 4,431,000		$ 779,000	$ 4,431,000
Stock compensation expense (reduction)							8,100,000		11,100,000		$ 21,900,000	$ 15,300,000
Leasehold impairment charge							970,000		180,000
Restructuring Reserve
Initial charge related to employee benefits, Beginning Balance				1,751,000	3,135,000				1,751,000
Additional charge	273,000		$ 393,000	$ 386,000	301,000	4,130,000	4,431,000		779,000	4,431,000
Payments for the period					(1,657,000)				(1,751,000)
Balance at the End of the year	$ 1,751,000	$ 3,135,000			$ 1,751,000	3,135,000	1,751,000	$ 3,135,000		$ 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 charge							4,400,000
One-time charge for severance							2,800,000
Benefit plan severance cost							593,000
Restructuring Reserve
Additional charge							$ 4,400,000
930 Winter Street, Walham, MA
Restructuring
Area of space leased | ft²	10,281				10,281		10,281			10,281
930 Winter Street, Walham, MA | Lease
Restructuring
Area of space leased | ft²	10,281				10,281		10,281			10,281
Estimated period to sub-lease								9 months
Leasehold impairment charge								$ 970,000	$ 779,000
Leasehold improvement cost		$ 193,000				$ 193,000		$ 193,000
Stock options
Restructuring
Forfeited (in shares) | shares							1,670,000		3,106,000		661,000
Granted (in shares) | shares							3,536,000		1,589,000		3,340,000
Stock options | Workforce reduction
Restructuring
Forfeited (in shares) | shares							762,000
Stock compensation expense (reduction)							$ (837,000)
Granted (in shares) | shares		847,000
Vesting period		3 years