| Accumulated Other Comprehensive Income (Parentheticals) (Details) $ in Millions | 6 Months Ended | 
|---|---|
| Jun. 30, 2018  USD ($) | |
| Statement Of Income And Comprehensive Income [Abstract] | |
| Amount expected to be reclassified into earnings | $ 49.3 | 
| X | ||||||||||
| 
- Definition The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
 | 
| X | ||||||||||
| 
- References No definition available. 
 |