Loans and Allowance for Credit Losses Loans and Allowance for Credit Losses (Balance of ALLL and Related Loans) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses	$ 1,643	$ (29,232)	$ (25,414)	$ (125,428)	$ 469	$ (1,839)	$ 2,747	$ (10,281)	$ (178,431)	$ (8,904)	$ (25,925)
Financing Receivable, Allowance for Credit Loss	257,323				108,671				257,323	108,671	109,931	$ 144,795
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					20,490					20,490
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					88,181					88,181
Financing Receivable, Individually Evaluated for Impairment					244,905					244,905
Financing Receivable, Collectively Evaluated for Impairment					22,743,323					22,743,323
Loans and Leases Receivable, Net of Deferred Income	23,866,042				23,154,988				23,866,042	23,154,988
US Government Agency Insured Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,419,074				698,644				1,419,074	698,644
Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss	18,719				11,154				18,719	11,154	10,788	10,720
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					9					9
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					11,145					11,145
Financing Receivable, Individually Evaluated for Impairment					57,117					57,117
Financing Receivable, Collectively Evaluated for Impairment					5,454,422					5,454,422
Loans and Leases Receivable, Net of Deferred Income	6,348,222				5,661,119				6,348,222	5,661,119
Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss	238,604				97,517				238,604	97,517	99,143	$ 134,075
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment					20,481					20,481
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment					77,036					77,036
Financing Receivable, Individually Evaluated for Impairment					187,788					187,788
Financing Receivable, Collectively Evaluated for Impairment					17,288,901					17,288,901
Loans and Leases Receivable, Net of Deferred Income	$ 17,517,820				17,493,869				17,517,820	17,493,869
Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss					0					0
Loans and Leases Receivable, Net of Deferred Income					166,760					166,760
Financial Asset Acquired with Credit Deterioration [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss					0					0
Loans and Leases Receivable, Net of Deferred Income					149,580					149,580
Financial Asset Acquired with Credit Deterioration [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing Receivable, Allowance for Credit Loss					0					0
Loans and Leases Receivable, Net of Deferred Income					$ 17,180					17,180
Funded Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses									(182,339)	(8,904)	(25,925)
Funded Loans [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses									(556)	(154)	(1,032)
Funded Loans [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses									(182,895)	$ (8,750)	$ (24,893)
Off Balance Sheet [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses									(5,572)
Accrued Interest Receivable
Financing Receivable, Allowance for Credit Loss [Line Items]
Provision for credit losses									$ (1,300)