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Condensed Financial Information of Registrant Condensed Financial Information of Registrant (Narratives) (Details) |  |  |  |  | 1 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 29, 2017 USD ($) | Mar. 08, 2017 USD ($) | Feb. 13, 2014 USD ($) | Aug. 09, 2013 USD ($) | Jan. 31, 2017 | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Jul. 31, 2018 | Jan. 31, 2018 | Jul. 07, 2017 | Dec. 31, 2016 USD ($)
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital distribution from subsidiaries |  |  |  |  |  | $ 5,200,000 | $ 6,000,000.0 |  |  |  |  |
Proceeds from dividends received |  |  |  |  |  | 114,431,433 | 135,000,000 | $ 109,000,000 |  |  |  |
Repayments of debt |  | $ 320,000,000 |  |  |  |  |  |  |  |  |  |
Swap [Member] | AFL [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Swap agreement collateral |  |  |  | $ 40,000,000 |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  |  |  |  |  |  | $ 152,000,000
Term of swap agreement |  |  |  | 3 years | 1 year |  |  |  |  |  |  |
Swap [Member] | AFL [Member] | LIBOR [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 1.35% | 1.28% |  |  | 1.35% |  |  | 1.28% |
Swap [Member] | FFL [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Swap agreement collateral |  |  | $ 31,000,000 |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |
Term of swap agreement |  |  | 1 year |  |  |  | 1 year |  |  |  |  |
Swap [Member] | FFL [Member] | LIBOR [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  | 1.28% |  |  |  | 1.28% |  | 1.05% | 1.20% |  |
Unsecured Notes One [Member] | Unsecured Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Unsecured debt |  |  |  |  |  | $ 375,000,000 |  |  |  |  |  |
Interest rate, stated percentage |  | 4.40% |  |  |  | 4.40% |  |  |  |  |  |
Debt issuance costs |  | $ 3,400,000 |  |  |  |  |  |  |  |  |  |
Discount percent |  | 99.847% |  |  |  |  |  |  |  |  |  |
Interest rate, effective percentage |  | 4.45% |  |  |  |  |  |  |  |  |  |
Unsecured Notes Two [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Loan maximum borrowing capacity | $ 50,000,000 |  |  |  |  |  |  |  |  |  |  |
Unsecured Notes Two [Member] | Unsecured Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Unsecured debt |  |  |  |  |  | $ 0 |  |  |  |  |  |
Minimum [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt to total capital ratio | 0.15 |  |  |  |  |  |  |  |  |  |  |
Commitment fee on undrawn portion of facility | 0.125% |  |  |  |  |  |  |  |  |  |  |
Minimum [Member] | LIBOR [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 1.125% |  |  |  |  |  |  |  |  |  |  |
Debt to total capital ratio | 0.15 |  |  |  |  |  |  |  |  |  |  |
Minimum [Member] | Unsecured Notes Two [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Commitment fee on undrawn portion of facility |  |  |  |  |  | 0.15% |  |  |  |  |  |
Minimum [Member] | Unsecured Notes Two [Member] | Unsecured Debt [Member] | LIBOR [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  | 0.1125% |  |  |  |  |  |
Maximum [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt to total capital ratio | 0.25 |  |  |  |  |  |  |  |  |  |  |
Commitment fee on undrawn portion of facility | 0.225% |  |  |  |  |  |  |  |  |  |  |
Maximum [Member] | LIBOR [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | 1.625% |  |  |  |  |  |  |  |  |  |  |
Debt to total capital ratio | 0.25 |  |  |  |  |  |  |  |  |  |  |
Maximum [Member] | Unsecured Notes Two [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Debt to total capital ratio |  |  |  |  |  | 0.172 |  |  |  |  |  |
Maximum [Member] | Unsecured Notes Two [Member] | Unsecured Debt [Member] | LIBOR [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  | 0.1625% |  |  |  |  |  |
Parent Company [Member] |  |  |  |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Capital distribution from subsidiaries |  |  |  |  |  | $ 30,068,567 | $ 0 | $ 0 |  |  |  |
Payments for contributions to subsidiaries |  |  |  |  |  | $ 125,000 | $ 540,619 | $ 140,125,000 |  |  |  |

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