Income Taxes - Components of provision for income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Provision for income tax benefit (expense)
Current	$ 10,561	$ (13,694)	$ (10,110)
Total	$ 10,561	$ (13,694)	$ (10,110)
Effective tax rate (as a percent)	4.67%	(5.04%)	(5.60%)
Provision for income taxes on undistributed earnings of foreign subsidiaries	$ 0
Undistributed earnings	0
United States
Provision for income tax benefit (expense)
Current	$ 10,563	$ (13,091)	$ (9,859)
Ireland
Provision for income tax benefit (expense)
Current		$ (566)	$ (219)
Effective tax rate (as a percent)	4.67%	(5.04%)	(5.60%)
United Kingdom
Provision for income tax benefit (expense)
Current	$ (2)	$ (37)	$ (32)