Income Taxes - Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of unrecognized tax benefits
Balance at the beginning of the year	$ 3,088	$ 0	$ 0
Additions for current year tax positions	0	7,719	0
Reductions for current year tax positions	0	(4,631)	0
Additions for prior year tax positions	4,631	0	2,337
Reductions for prior year tax positions	(7,719)	0	(2,337)
Balance at the end of the year	$ 0	$ 3,088	$ 0