Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	$ 395,706	$ 324,130	$ 1,125,874	$ 1,030,612
Provision for (reversal of) credit losses	(10,000)	10,000	(25,000)	186,313
Noninterest income	73,109	54,503	214,406	165,715
Noninterest expense	205,384	172,573	585,984	537,671
Segment income (loss) before income taxes	273,431	196,060	779,296	472,343
Segment net income	225,449	159,537	655,185	403,713
Segment assets	60,959,110	50,371,477	60,959,110	50,371,477	$ 52,156,913
Consumer and Business Banking
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	176,678	120,969	500,352	398,486
Provision for (reversal of) credit losses	1,293	(3,470)	(598)	9,908
Noninterest income	22,446	17,426	67,728	47,771
Noninterest expense	90,575	81,419	267,511	248,547
Segment income (loss) before income taxes	107,256	60,446	301,167	187,802
Segment net income	76,825	43,310	215,720	134,563
Segment assets	14,687,023	12,838,625	14,687,023	12,838,625
Commercial Banking
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	189,791	162,884	559,579	530,181
Provision for (reversal of) credit losses	(11,293)	13,470	(24,402)	176,405
Noninterest income	42,925	28,984	125,487	95,327
Noninterest expense	66,688	61,863	200,109	196,889
Segment income (loss) before income taxes	177,321	116,535	509,359	252,214
Segment net income	126,767	83,340	364,632	180,649
Segment assets	27,861,690	26,526,173	27,861,690	26,526,173
Other
Segment Reporting Information
Net interest income before provision for (reversal of) credit losses	29,237	40,277	65,943	101,945
Provision for (reversal of) credit losses	0	0	0	0
Noninterest income	7,738	8,093	21,191	22,617
Noninterest expense	48,121	29,291	118,364	92,235
Segment income (loss) before income taxes	(11,146)	19,079	(31,230)	32,327
Segment net income	21,857	32,887	74,833	88,501
Segment assets	$ 18,410,397	$ 11,006,679	$ 18,410,397	$ 11,006,679