Reportable Operating Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Selected business segment financial information
Net interest income (expense)	$ 530,559	$ 535,734	$ 573,402
Benefit (Provision) for credit losses	39,000	(121,718)	(13,800)
Net interest income (expense) after benefit for credit losses	569,559	414,016	559,602
Noninterest income	184,916	197,380	192,533
Noninterest expense	(405,479)	(367,672)	(370,437)
Income before provision for income taxes	348,996	243,724	381,698
Benefit for income taxes	(83,261)	(57,970)	(97,306)
Net income	265,735	185,754	284,392
Total assets	24,992,410	22,662,831	20,166,734
Retail Banking
Selected business segment financial information
Net interest income (expense)	385,656	375,145	413,029
Benefit (Provision) for credit losses	16,267	(52,719)	(6,248)
Net interest income (expense) after benefit for credit losses	401,923	322,426	406,781
Noninterest income	91,672	98,026	95,413
Noninterest expense	(247,949)	(232,976)	(228,389)
Income before provision for income taxes	245,646	187,476	273,805
Benefit for income taxes	(58,710)	(43,825)	(69,285)
Net income	186,936	143,651	204,520
Total assets	7,148,376	6,894,602	7,276,047
Commercial Banking
Selected business segment financial information
Net interest income (expense)	162,997	151,622	141,227
Benefit (Provision) for credit losses	22,452	(53,921)	(7,552)
Net interest income (expense) after benefit for credit losses	185,449	97,701	133,675
Noninterest income	72,781	78,202	73,635
Noninterest expense	(100,932)	(79,961)	(82,380)
Income before provision for income taxes	157,298	95,942	124,930
Benefit for income taxes	(37,525)	(21,951)	(32,298)
Net income	119,773	73,991	92,632
Total assets	5,972,567	6,526,863	6,071,356
Treasury and Other
Selected business segment financial information
Net interest income (expense)	(18,094)	8,967	19,146
Benefit (Provision) for credit losses	281	(15,078)
Net interest income (expense) after benefit for credit losses	(17,813)	(6,111)	19,146
Noninterest income	20,463	21,152	23,485
Noninterest expense	(56,598)	(54,735)	(59,668)
Income before provision for income taxes	(53,948)	(39,694)	(17,037)
Benefit for income taxes	12,974	7,806	4,277
Net income	(40,974)	(31,888)	(12,760)
Total assets	$ 11,871,467	$ 9,241,366	$ 6,819,331