Marketable Securities (Contractual Maturities Of Marketable Securities) (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Marketable Securities [Abstract]
Due in one year or less, Amortized Cost	$ 169,044
Due after one through two years, Amortized Cost	67,951
Total marketable securities, Amortized Cost	236,995
Due in one year or less, Fair Value	169,002
Due after one through two years, Fair Value	67,947
Total marketable securities, Fair Value	$ 236,949