Borrowings - MetLife Facility (Narrative) (Details) - USD ($)  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020  | 
Feb. 20, 2020  | 
Dec. 31, 2019  | 
|
| Debt Instrument [Line Items] | |||
| Debt instrument, loans to value ratios percentage | 60.00% | ||
| MetLife Credit Facility | |||
| Debt Instrument [Line Items] | |||
| Debt instrument, face amount | $ 200,000,000.0 | ||
| Line of credit facility, maximum borrowing capacity | 75,000,000.0 | ||
| Debt instrument, loans to value ratios percentage | 60.00% | ||
| MetLife Credit Facility | Notes payable to bank | |||
| Debt Instrument [Line Items] | |||
| Debt instrument, face amount | $ 75,000,000 | $ 75,000,000.0 | |
| Undrawn commitment | $ 38,100,000 | $ 21,500,000 | 
| X | ||||||||||
- Definition Debt Instrument, Loans To Value Ratios Percentage No definition available. 
  | 
| X | ||||||||||
- Definition Face (par) amount of debt instrument at time of issuance. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
  | 
| X | ||||||||||
- Definition Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- Details 
  | 
| X | ||||||||||
- Details 
  |