Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation allowance
Deferred tax assets, valuation allowance	$ 122,147	$ 120,801
Net increase in valuation allowance	1,300	0
Reconciliation of the total amounts of unrecognized tax benefits
Unrecognized tax benefit at the beginning of the period	36,243	34,065
Gross increases—tax positions in current year	5,232	2,178
Unrecognized tax benefit at the end of the period	41,475	36,243	$ 34,065
Additional information on income tax
Accrued interest expense and penalties	0
Interest expense related to uncertain tax positions	$ 0	$ 0	$ 100