Income Taxes - Unrealized tax benefits and others (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Non-current liability related to uncertain tax positions	$ 0
Reconciliation of the gross unrealized tax benefits
Unrecognized tax benefits, beginning of year	8,340	$ 6,839	$ 5,306
Gross increases—tax positions from prior periods	(40)	(31)	34
Gross increases - tax positions from current period	2,004	1,532	1,499
Unrecognized tax benefits, end of year	10,304	$ 8,340	$ 6,839
Excess of the amount of net income for financial reporting over the tax basis of investments in foreign subsidiaries	$ 10,800
Minimum
Reconciliation of the gross unrealized tax benefits
Foreign statutes of limitation	2 years
Maximum
Reconciliation of the gross unrealized tax benefits
Foreign statutes of limitation	4 years