Merger - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Combinations [Abstract]
Net interest income and other noninterest income	$ 536,165	$ 570,396	$ 1,654,571	$ 1,693,537
Net income	125,560	156,977	435,003	434,686
Net income available to common shareholders	$ 123,066	$ 154,483	$ 427,522	$ 422,111
Earnings per share:
Basic (in usd per share)	$ 0.81	$ 1.00	$ 2.79	$ 2.71
Diluted (in usd per share)	$ 0.81	$ 0.99	$ 2.77	$ 2.69