Debt and Credit Facilities (Schedule of Convertible Debt Interest Expense) (Details) - Convertible Senior Notes due 2022 $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Coupon interest expense	$ 661
Amortization of debt discount - equity component	330
Amortization of debt discount - initial purchaser	98
Amortization of transaction costs	16
Total interest expense	$ 1,105