Merger - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Combinations [Abstract]
Net interest income and other noninterest income	$ 495,977	$ 536,165	$ 1,545,834	$ 1,654,571
Net income	55,738	125,560	131,401	435,003
Net income available to common shareholders	$ 53,244	$ 123,066	$ 123,920	$ 427,522
Earnings per share:
Basic (in usd per share)	$ 0.35	$ 0.81	$ 0.82	$ 2.79
Diluted (in usd per share)	$ 0.35	$ 0.81	$ 0.82	$ 2.77