Fair Value Measurements (Narrative) (Details) - USD ($) |
3 Months Ended | 9 Months Ended | ||
---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|
Fair Value Measurements [Abstract] | ||||
Transfers of assets and liabilities between level 1, 2, 3 | $ 0 | $ 0 | $ 0 | $ 0 |