Fair Value Measurements - Valuation Techniques and Unobservable Inputs Related to Level 3 Assets (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	$ 501,292	$ 242,762
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	$ 501,292	$ 242,762
Level 3 | Valuation, Market Approach | Measurement Input Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Individually evaluated loans requiring allowance, net	0.080
Real estate owned, net	0.080	0.080
Collateral dependent impaired loans requiring specific allowance, net		0.080
Level 3 | Valuation, Market Approach | Weighted Average | Measurement Input Selling Cost
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Individually evaluated loans requiring allowance, net	0.080
Real estate owned, net	0.080	0.080
Collateral dependent impaired loans requiring specific allowance, net		0.080
Level 3 | Discounted Cash Flow | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.105	0.105
Interest-only strips	0.150	0.150
Level 3 | Discounted Cash Flow | Prepayment Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.150	0.150
Level 3 | Discounted Cash Flow | Default Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.010	0.010
Level 3 | Discounted Cash Flow | Loss Severity Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.100	0.100
Level 3 | Discounted Cash Flow | Minimum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for sale	0.120	0.120
Level 3 | Discounted Cash Flow | Minimum | Collateral Value (% of UPB)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.080	0.18
Level 3 | Discounted Cash Flow | Minimum | Timing of Resolution/Payoff
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment,at fair value	5 months	5 months
Loans held for sale	0 months	0 months
Interest-only strips	0 months	0 months
Level 3 | Discounted Cash Flow | Maximum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for sale	0.150	0.150
Level 3 | Discounted Cash Flow | Maximum | Collateral Value (% of UPB)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.970	0.94
Level 3 | Discounted Cash Flow | Maximum | Timing of Resolution/Payoff
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment,at fair value	212 months	218 months
Loans held for sale	13 months	12 months
Interest-only strips	13 months	7 months
Level 3 | Discounted Cash Flow | Weighted Average | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.105	0.105
Loans held for sale	0.145	0.147
Interest-only strips	0.150	0.150
Level 3 | Discounted Cash Flow | Weighted Average | Collateral Value (% of UPB)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.880	0.870
Level 3 | Discounted Cash Flow | Weighted Average | Timing of Resolution/Payoff
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment,at fair value	60 months	65 months
Loans held for sale	7 months 18 days	7 months
Interest-only strips	2 months 12 days	2 months 3 days
Level 3 | Discounted Cash Flow | Weighted Average | Prepayment Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.150	0.150
Level 3 | Discounted Cash Flow | Weighted Average | Default Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.010	0.010
Level 3 | Discounted Cash Flow | Weighted Average | Loss Severity Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loans held for investment, at fair value	0.100	0.100
Level 3 | Individually evaluated loans requiring allowance net
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	$ 269,499
Level 3 | Real Estate Owned, Net
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	15,648	$ 13,068
Level 3 | Loans Held for Investment
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	2,956	2,960
Level 3 | Loans Held for Sale
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	212,344	214,467
Level 3 | Interest-only Strips
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements	$ 845	894
Level 3 | Collateral Dependent Impaired Loans
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total recurring fair value measurements		$ 11,373