Fair Values (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible 2022 note hedge asset	$ 54,858,000	$ 46,915,000
Convertible Debt Bond Hedge [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible 2022 note hedge asset	54,858,000	46,915,000
Forward exchange contracts—net | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	0	0
Forward exchange contracts—net | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	834,000	(1,390,000)
Forward exchange contracts—net | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	0	0
Convertible Debt Conversion Feature [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	0	0
Convertible Debt Conversion Feature [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	0	0
Convertible Debt Bond Hedge [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	0	0
Convertible Debt Bond Hedge [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair value, net	$ 0	$ 0