Long-term Debt and Short-term Borrowings (Components of Short-term Borrowings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Total balance at December 31,	$ 887,692	$ 261,190	$ 159,699
Weighted average interest rate at December 31,	1.93%	0.65%	0.08%
Maximum month end balance during the year	$ 887,692	$ 390,044	$ 414,245
Average amount outstanding during the year	$ 371,933	$ 256,011	$ 278,273
Weighted average interest rate during the year	0.96%	0.37%	0.18%