Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018
Income Taxes
TCJA of 2017 provisional income tax expense		$ 27,600
Period over which NOL and tax credit carryforward limitations are applied	1 year
Unrecognized tax benefits from uncertain tax	$ 0	$ 0	$ 0
Period over which material changes in unrecognized tax positions are not expected	12 months
Federal
Income Taxes
Cumulative net operating loss carryforwards	$ 295,800
Percentage of taxable income that can be used to offset future taxable periods as a result of the TCJA	80.00%
Unlimited carryforward	$ 98,400
Tax credit carryforwards	21,600
State
Income Taxes
Cumulative net operating loss carryforwards	290,200
Tax credit carryforwards	$ 1,900
State | Massachusetts
Income Taxes
Carryforward term	20 years
Potential amount that may expire in a future period	$ 21,000
State | Pennsylvania
Income Taxes
Carryforward term	20 years