Loans Held For Investment And The Allowance For Credit Losses - Summary Of Amortized Cost By Origination Year Grouped By Risk Rating for Loans Held for Investment Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, One	$ 1,065,678	$ 247,770
Amortized cost basis of loans by origination year, Two	255,642	2,171,469
Amortized cost basis of loans by origination year, Three	1,789,490	1,515,229
Amortized cost basis of loans by origination year, Four	1,061,789	556,883
Amortized cost basis of loans by origination year, Five	553,681	25,049
Amortized cost basis of loans by origination year, Prior	23,009
Amortized cost basis of loans by origination year, Total	4,749,289	4,516,400
Rating 2
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Total	86,286	337,738
Rating 3
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Total	4,169,783	3,340,663
Rating 4
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Total	462,020	806,893
Rating 5
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Total	31,200	31,106
Senior Loans
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, One	1,065,678	247,770
Amortized cost basis of loans by origination year, Two	255,642	2,139,117
Amortized cost basis of loans by origination year, Three	1,754,561	1,515,229
Amortized cost basis of loans by origination year, Four	1,061,789	556,883
Amortized cost basis of loans by origination year, Five	553,681	25,049
Amortized cost basis of loans by origination year, Prior	23,009
Amortized cost basis of loans by origination year, Total	4,714,360	4,484,048
Senior Loans | Rating 2
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, One	33,590
Amortized cost basis of loans by origination year, Three		337,738
Amortized cost basis of loans by origination year, Four	52,696
Amortized cost basis of loans by origination year, Total	86,286	337,738
Senior Loans | Rating 3
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, One	1,032,088	247,770
Amortized cost basis of loans by origination year, Two	255,642	1,705,783
Amortized cost basis of loans by origination year, Three	1,556,049	1,099,503
Amortized cost basis of loans by origination year, Four	930,927	255,255
Amortized cost basis of loans by origination year, Five	337,139
Amortized cost basis of loans by origination year, Prior	23,009
Amortized cost basis of loans by origination year, Total	4,134,854	3,308,311
Senior Loans | Rating 4
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Two		433,334
Amortized cost basis of loans by origination year, Three	198,512	46,882
Amortized cost basis of loans by origination year, Four	46,966	301,628
Amortized cost basis of loans by origination year, Five	216,542	25,049
Amortized cost basis of loans by origination year, Total	462,020	806,893
Senior Loans | Rating 5
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Three		31,106
Amortized cost basis of loans by origination year, Four	31,200
Amortized cost basis of loans by origination year, Total	31,200	31,106
Subordinated and Mezzanine Loans
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Two		32,352
Amortized cost basis of loans by origination year, Three	34,929
Amortized cost basis of loans by origination year, Total	34,929	32,352
Subordinated and Mezzanine Loans | Rating 3
Accounts Notes And Loans Receivable [Line Items]
Amortized cost basis of loans by origination year, Two		32,352
Amortized cost basis of loans by origination year, Three	34,929
Amortized cost basis of loans by origination year, Total	$ 34,929	$ 32,352