Debt And Interest Expense (Credit Facilities) (Narrative) (Details) |
12 Months Ended |
|---|---|
|
Dec. 31, 2018
USD ($)
| |
| Debt Instrument [Line Items] | |
| Borrowing capacity of senior unsecured revolving credit facility | $ 200,000,000.0 |
| Credit facility, maturity date | Apr. 01, 2020 |
| Aggregate increase of commitment amount available | $ 150,000,000.0 |
| Minimum [Member] | |
| Debt Instrument [Line Items] | |
| Interest coverage ratio | 3.0 |
| Maximum [Member] | |
| Debt Instrument [Line Items] | |
| Leverage ratio | 2.5 |