Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	$ 324,130	$ 369,807	$ 1,030,612	$ 1,099,594
Provision for (reversal of) credit losses	10,000	38,284	186,313	80,108
Noninterest Income	49,580	51,474	162,266	146,364
Noninterest expense	167,650	176,630	534,222	541,215
Segment income before income taxes	196,060	206,367	472,343	624,635
Segment net income	159,537	171,416	403,713	485,820
Segment assets	50,371,477	43,274,659	50,371,477	43,274,659	$ 44,196,096
Consumer and Business Banking
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	120,969	170,183	398,486	536,153
Provision for (reversal of) credit losses	(3,470)	4,251	9,908	8,880
Noninterest Income	17,426	15,103	47,771	43,378
Noninterest expense	81,419	86,489	248,547	258,051
Segment income before income taxes	60,446	94,546	187,802	312,600
Segment net income	43,310	67,592	134,563	223,478
Segment assets	12,838,625	11,277,171	12,838,625	11,277,171
Commercial Banking
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	162,884	166,106	530,181	477,755
Provision for (reversal of) credit losses	13,470	34,033	176,405	71,228
Noninterest Income	28,984	33,731	95,327	91,931
Noninterest expense	61,863	62,246	196,889	200,093
Segment income before income taxes	116,535	103,558	252,214	298,365
Segment net income	83,340	74,111	180,649	213,331
Segment assets	26,526,173	24,885,849	26,526,173	24,885,849
Other
Segment Reporting Information
Net interest income before (reversal of) provision for credit losses	40,277	33,518	101,945	85,686
Provision for (reversal of) credit losses	0	0	0	0
Noninterest Income	3,170	2,640	19,168	11,055
Noninterest expense	24,368	27,895	88,786	83,071
Segment income before income taxes	19,079	8,263	32,327	13,670
Segment net income	32,887	29,713	88,501	49,011
Segment assets	$ 11,006,679	$ 7,111,639	$ 11,006,679	$ 7,111,639