Long-Term Debt and Interest Expense - Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Finance leases and other notes	$ 55,630	$ 60,909
Unamortized discounts and deferred financing costs	(10,807)	(11,169)
Total long-term debt	344,823	349,740
Less current portion	22,465	27,039
Total non-current portion of long-term debt	322,358	322,701
10.75% Senior Notes due 2023
Debt Instrument [Line Items]
Long-term debt, gross	$ 300,000	$ 300,000