Long-Term Debt (Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Coupon interest	$ 12,188	$ 11,240
Amortization of debt issuance costs	1,424	1,305	$ 0
Total interest expense on Notes	$ 13,612	$ 12,545