Reportable Segments - Summary of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Aug. 01, 2019	Dec. 31, 2018
Segment Reporting Information
Net interest income (expense)	$ 371,793	$ 253,502	$ 880,279	$ 755,342
Provision for credit losses	27,188	2,270	50,879	27,874
Net interest income after provision for credit losses	344,605	251,232	829,400	727,468
Noninterest income	94,258	112,064	307,480	330,529
Noninterest expense	425,620	246,423	915,544	764,442
Income tax (benefit) expense	(11,735)	28,034	28,866	66,083
Income after income tax (benefit) expense	24,978	88,839	192,470	227,472
Income attributable to non-controlling interest	2,830	2,643	9,401	8,766
Preferred stock dividends	2,494	2,494	7,481	9,094
Impact of preferred stock redemption	0	0	0	3,481
Net income available to common shareholders	19,654	83,702	175,588	206,131
Total assets	45,692,511	22,904,785	45,692,511	22,904,785		$ 23,699,612
Goodwill	1,265,111		1,265,111		$ 1,110,354	$ 154,757
Consumer Banking
Segment Reporting Information
Net interest income (expense)	191,940	143,015	470,738	429,132
Provision for credit losses	4,489	(953)	16,406	18,900
Net interest income after provision for credit losses	187,451	143,968	454,332	410,232
Noninterest income	57,102	66,621	183,767	196,827
Noninterest expense	210,728	162,034	520,007	511,915
Income tax (benefit) expense	6,817	11,613	26,529	23,037
Income after income tax (benefit) expense	27,008	36,942	91,563	72,107
Income attributable to non-controlling interest	0	0	0	0
Preferred stock dividends	0	0	0	0
Impact of preferred stock redemption				0
Net income available to common shareholders	27,008	36,942	91,563	72,107
Total assets	14,906,457	8,226,522	14,906,457	8,226,522
Commercial Banking
Segment Reporting Information
Net interest income (expense)	157,437	94,252	350,848	289,315
Provision for credit losses	22,699	3,223	34,473	8,974
Net interest income after provision for credit losses	134,738	91,029	316,375	280,341
Noninterest income	47,929	44,934	132,883	132,794
Noninterest expense	102,841	77,863	267,147	229,094
Income tax (benefit) expense	8,172	12,813	30,271	40,505
Income after income tax (benefit) expense	71,654	45,287	151,840	143,536
Income attributable to non-controlling interest	2,830	2,643	9,401	8,766
Preferred stock dividends	0	0	0	0
Impact of preferred stock redemption				0
Net income available to common shareholders	68,824	42,644	142,439	134,770
Total assets	22,076,203	11,553,453	22,076,203	11,553,453
Enterprise Services
Segment Reporting Information
Net interest income (expense)	22,416	16,235	58,693	36,895
Provision for credit losses	0	0	0	0
Net interest income after provision for credit losses	22,416	16,235	58,693	36,895
Noninterest income	(10,773)	509	(9,170)	908
Noninterest expense	112,051	6,526	128,390	23,433
Income tax (benefit) expense	(26,724)	3,608	(27,934)	2,541
Income after income tax (benefit) expense	(73,684)	6,610	(50,933)	11,829
Income attributable to non-controlling interest	0	0	0	0
Preferred stock dividends	2,494	2,494	7,481	9,094
Impact of preferred stock redemption				3,481
Net income available to common shareholders	(76,178)	4,116	(58,414)	(746)
Total assets	$ 8,709,851	$ 3,124,810	$ 8,709,851	$ 3,124,810