Unfunded Loan Commitments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jan. 01, 2020	Dec. 31, 2018
Credit Loss [Abstract]
Contractual obligation	$ 1,800,000		$ 1,800,000
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,929,323	$ 383,997	441,912	$ 341,121	$ 341,121
Less: provisions for credit losses	(3,640)	99,526	409,505	256,691
Transfer of allowance for funded loans	(60,666)	(76,227)	(178,120)	(205,916)
Ending Balance	1,734,559	414,406	1,734,559	414,406	441,912
Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Day 1 adjustment for the adoption of CECL						$ 1,143,053
Unfunded Commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,119,042	1,335,755	1,910,603	2,010,744	2,010,744
Less: provisions for credit losses	2,542,390	3,140,432	4,542,560	5,122,672
Transfer of allowance for funded loans	(1,890,305)	(2,242,077)	(4,682,036)	(4,899,306)
Ending Balance	1,771,127	2,234,110	1,771,127	2,234,110	1,910,603
Unfunded Commitments | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Day 1 adjustment for the adoption of CECL					0		$ 0
Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	85,958	755
Less: provisions for credit losses	129,290	3,382
Transfer of allowance for funded loans	(100,470)	(2,170)
Ending Balance	114,778	1,967	114,778	1,967
Consumer Portfolio Segment | Unfunded Commitments
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			2,481	2,165	2,165
Less: provisions for credit losses			276,094	5,516
Transfer of allowance for funded loans			(279,555)	(5,714)
Ending Balance	$ 114,778	$ 1,967	$ 114,778	$ 1,967	2,481
Consumer Portfolio Segment | Unfunded Commitments | Cumulative Effect, Period Of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Day 1 adjustment for the adoption of CECL					$ 115,758		$ 0