Restructuring Charges (Details)	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2018 employee	Sep. 30, 2016 ft²	Feb. 29, 2016 ft²
Workforce reduction
Restructuring
One-time charge for severance	$ 1,200,000
Benefit plan severance cost		$ 1,100,000
930 Winter Street, Walham, MA
Restructuring
Area of space leased | ft²						10,281
930 Winter Street, Walham, MA | Lease
Restructuring
Area of space leased | ft²					10,281
Leasehold impairment charge		$ 0	$ 386,000
Forecast | Workforce reduction
Restructuring
Approximate positions to be eliminated | employee				30
Approximate current positions to be eliminated | employee				20
Stock options | Workforce reduction
Restructuring
Stock compensation expense (reduction)	$ 157,000