Debt - Senior Unsecured Notes - Narrative (Details) - Unsecured Debt - USD ($) |
Aug. 18, 2016 |
Jun. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|---|
| Debt Instrument [Line Items] | |||
| Aggregate principal amount of debt | $ 300,000,000 | ||
| Principal amount issued | 99.378% | ||
| Proceeds from issuance of debt | $ 296,200,000 | ||
| Stated interest rate | 4.45% | ||
| Deferred financing costs | $ 3,400,000 | $ 4,800,000 | |
| Unamortized discount | $ 1,900,000 | 1,600,000 | $ 1,700,000 |
| Unamortized deferred financing costs | $ 2,900,000 | $ 3,000,000 | |
| Period Prior to June 15, 2026 | |||
| Debt Instrument [Line Items] | |||
| Redemption price, percent of principal amount | 100.00% |