Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	$ 376,473	$ 343,775	$ 730,168	$ 706,482
Provision for (reversal of) credit losses	(15,000)	102,443	(15,000)	176,313
Noninterest income	68,431	55,707	141,297	111,213
Noninterest expense	189,523	184,766	380,600	365,099
Segment income (loss) before income taxes	270,381	112,273	505,865	276,283
Segment net income	224,742	99,352	429,736	244,176
Segment assets	59,854,876	49,407,593	59,854,876	49,407,593	$ 52,156,913
Consumer and Business Banking
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	173,775	124,926	323,674	277,517
Provision for (reversal of) credit losses	2,358	5,590	(1,891)	13,378
Noninterest income	24,454	13,943	45,282	30,345
Noninterest expense	87,650	80,164	176,936	167,128
Segment income (loss) before income taxes	108,221	53,115	193,911	127,356
Segment net income	77,517	38,058	138,895	91,253
Segment assets	14,594,087	12,666,938	14,594,087	12,666,938
Commercial Banking
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	192,696	183,796	369,788	367,297
Provision for (reversal of) credit losses	(17,358)	96,853	(13,109)	162,935
Noninterest income	32,552	33,887	82,562	66,343
Noninterest expense	64,164	64,900	133,421	135,026
Segment income (loss) before income taxes	178,442	55,930	332,038	135,679
Segment net income	127,785	40,178	237,865	97,309
Segment assets	27,354,253	26,984,013	27,354,253	26,984,013
Other
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	10,002	35,053	36,706	61,668
Provision for (reversal of) credit losses	0	0	0	0
Noninterest income	11,425	7,877	13,453	14,525
Noninterest expense	37,709	39,702	70,243	62,945
Segment income (loss) before income taxes	(16,282)	3,228	(20,084)	13,248
Segment net income	19,440	21,116	52,976	55,614
Segment assets	$ 17,906,536	$ 9,756,642	$ 17,906,536	$ 9,756,642