Commitments and Contingencies - Letters of Credit (Details) - USD ($) |
Dec. 31, 2017 |
Aug. 03, 2015 |
|---|---|---|
| Line of Credit Facility [Line Items] | ||
| Line of credit, amount to be issued | $ 100,000,000 | |
| $2.2 Million Standby Letters of Credit | ||
| Line of Credit Facility [Line Items] | ||
| Line of credit, amount to be issued | $ 2,190,000.00 | |
| $1.7 Million Standby Letters of Credit | ||
| Line of Credit Facility [Line Items] | ||
| Line of credit, amount to be issued | $ 1,700,000.0 |