Fair Value Measurements (Derivative Financial Instruments) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative [Line Items]
Cash held as collateral	$ 0		$ 0		$ 1,451,000
Foreign currency derivative contracts
Derivative [Line Items]
Notional amount of foreign currency derivative contracts	0		0		2,866,000
Fair value of foreign currency derivatives contracts	0		0		$ 63,000
Foreign currency derivative contracts | Other (income) expense
Derivative [Line Items]
Gain (losses) on Derivative Instruments Recognized in Statements of Operations	$ 0	$ (19,000)	$ (50,000)	$ 194,000