Long-Term Debt - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Long-Term Debt
Coupon interest at 3.75%	$ 12,188	$ 12,188	$ 12,188
Amortization of debt issuance costs	1,424	1,424	1,424
Total interest expense on Notes	$ 13,612	$ 13,612	$ 13,612