Restructuring Charge (Details)	1 Months Ended		3 Months Ended
	Feb. 28, 2018 employee	Jan. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Workforce reduction
Restructuring
Approximate positions to be eliminated | employee	22
One-time charge for severance				$ 1,200,000
Benefit plan severance cost		$ 384,000
Restructuring charge
Balance at beginning of the period			$ 841,000
Payments during the period			(624,000)
Balance at end of the period			$ 217,000
Unoccupied office space for sub-lease			10,281
Workforce reduction | Stock options
Restructuring
Stock compensation expense				157,000
Lease
Restructuring charge
Leasehold impairment charge			$ 559,000	$ 0