ITG Acquisition - Pro Forma Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Revenue	$ 1,530,082	$ 1,878,718	$ 1,027,982
Net income (loss)	(103,705)	620,192	18,898
Net income (loss) available for common stockholders	(58,595)	289,441	$ 2,939
Pro Forma
Business Acquisition [Line Items]
Revenue	1,605,340	2,388,194
Net income (loss)	(94,233)	514,821
Net income (loss) available for common stockholders	$ (53,243)	$ 240,265