Unfunded Loan Commitments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Credit Loss [Abstract]
Contractual obligation		$ 1,700,000
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning Balance	$ 441,912	441,912	$ 341,121	$ 251,475
Provision/New commitments - net	121,000	93,133
Transfer - funded loans		(245,043)	(284,114)	(175,526)
Ending Balance		1,361,723	441,912	341,121
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning Balance	1,584,965	1,584,965
Day 1 adjustment for the adoption of CECL			1,143,053
Ending Balance			1,584,965
Unfunded Loan Commitment
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning Balance	1,910,603	1,910,603	2,010,744	1,838,840
Provision/New commitments - net		5,070,175	5,513,790	5,474,284
Transfer - funded loans		(5,307,760)	(5,613,931)	(5,302,380)
Ending Balance		1,673,018	1,910,603	2,010,744
Unfunded Loan Commitment | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning Balance	1,910,603	1,910,603
Day 1 adjustment for the adoption of CECL			0
Ending Balance			1,910,603
Consumer Portfolio Segment | Unfunded Loan Commitment
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning Balance	2,481	2,481	2,165	1,885
Provision/New commitments - net		312,613	6,533	5,611
Transfer - funded loans		(320,808)	(6,217)	(5,331)
Ending Balance		110,044	2,481	$ 2,165
Consumer Portfolio Segment | Unfunded Loan Commitment | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning Balance	$ 118,239	$ 118,239
Day 1 adjustment for the adoption of CECL			115,758
Ending Balance			$ 118,239