Income Taxes - Income tax expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax expense
Current income tax expense	$ (539)	$ 33,615	$ 26,261
Deferred income benefit	(101,927)	(1,304)
Total income tax expense	$ (102,466)	$ 32,311	$ 26,261