Long-Term Debt - Deferred Financing Activity (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Deferred Financing Activity [Roll Forward]
Beginning balance	$ 34,423	$ 38,766
Additions	4,956	10,275
Early Extinguishment	(1,395)	(4,207)
Amortized	(4,936)	(10,411)
Ending balance	33,048	34,423
Senior Notes | 2019 Notes
Deferred Financing Activity [Roll Forward]
Beginning balance	0	2,877
Additions		0
Early Extinguishment		(1,877)
Amortized		(1,000)
Ending balance		0
Senior Notes | 2020 Notes
Deferred Financing Activity [Roll Forward]
Beginning balance	5,380	11,209
Additions	0	0
Early Extinguishment	(1,395)	(2,330)
Amortized	(1,326)	(3,499)
Ending balance	2,659	5,380
Senior Notes | 2022 Private Placement Notes
Deferred Financing Activity [Roll Forward]
Beginning balance	602	752
Additions	0	0
Early Extinguishment	0	0
Amortized	(75)	(150)
Ending balance	527	602
Senior Notes | 2022 Notes
Deferred Financing Activity [Roll Forward]
Beginning balance	12,799	16,067
Additions	0	0
Early Extinguishment	0	0
Amortized	(1,634)	(3,268)
Ending balance	11,165	12,799
Senior Notes | 2023 Notes
Deferred Financing Activity [Roll Forward]
Beginning balance	3,922	4,762
Additions	0	0
Early Extinguishment	0	0
Amortized	(420)	(840)
Ending balance	3,502	3,922
Senior Notes | 2024 Notes
Deferred Financing Activity [Roll Forward]
Beginning balance	0
Additions	4,956
Early Extinguishment	0
Amortized	(75)
Ending balance	4,881	0
Term Loan | Term Loan
Deferred Financing Activity [Roll Forward]
Beginning balance	9,662	0
Additions		10,275
Early Extinguishment	0	0
Amortized	(920)	(613)
Ending balance	8,742	9,662
Revolving Credit Facility | Line of Credit
Deferred Financing Activity [Roll Forward]
Beginning balance	2,058	3,099
Additions	0	0
Early Extinguishment	0	0
Amortized	(486)	(1,041)
Ending balance	$ 1,572	$ 2,058