Acquisitions - Pro Forma Information Operations as Acquisition of NTA (Details) - NTA - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total revenues	$ 1,175,977	$ 1,339,896
Total expenses	967,352	1,288,690
Income before income taxes	208,625	51,206
Net income	$ 161,463	$ 43,373
Earnings Per Share [Abstract]
Basic (in usd per share)	$ 3.87	$ 1.04
Diluted (in usd per share)	$ 3.85	$ 1.04