Related Party Transactions - Investments in SMTA (Details) - USD ($) |
3 Months Ended | 12 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
May 31, 2018 |
Oct. 03, 2017 |
Sep. 30, 2019 |
Jun. 30, 2019 |
Mar. 31, 2019 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2020 |
|
| Related Party Transaction [Line Items] | ||||||||
| Preferred stock, shares issued | 6,900,000 | 6,900,000 | ||||||
| Dividend rate | 6.00% | |||||||
| Preferred dividend income from SMTA | $ 3,302,000 | $ 3,750,000 | $ 3,750,000 | $ 10,802,000 | $ 8,750,000 | |||
| Spirit MTA REIT | Affiliated Entity | ||||||||
| Related Party Transaction [Line Items] | ||||||||
| Preferred stock, shares issued | 6,000,000.0 | |||||||
| Aggregate liquidation preference amount | $ 150,000,000.0 | |||||||
| Dividend rate | 10.00% | |||||||
| Liquidation value on an annual basis (in USD per share) | $ 25.00 | |||||||
| Preferred dividend income from SMTA | $ 10,800,000 | $ 8,800,000 | ||||||