Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value) (Details) - Recurring - Marketable securities - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Net Asset (Liability) [Abstract]
Marketable securities	$ 35,156	$ 37,918
Level 1
Fair Value, Net Asset (Liability) [Abstract]
Marketable securities	35,156	37,918
Level 2
Fair Value, Net Asset (Liability) [Abstract]
Marketable securities	0	0
Level 3
Fair Value, Net Asset (Liability) [Abstract]
Marketable securities	$ 0	$ 0