Debt (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Long term debt and capital lease obligations
Current		$ 21,939		$ 21,939		$ 24,937
Debt		276,781		276,781		433,889
Finance Lease, Interest Expense		1,210	$ 512	3,459	$ 1,551
Interest expenses incurred for various debt instruments
Interest paid on Senior Notes due 2024		3,563	3,672	10,907	11,016
Interest paid on Revolving Credit Facility		963	1,515	4,769	4,035
Amortization of Debt Issuance Costs		378	323	1,110	972
Accretion		182	329	541	980
Interest Expense, Debt		58	196	60	312
Capitalized interest		(374)	(729)	(1,587)	(1,065)
Total interest expense, net of capitalized interest		5,980	$ 5,818	19,259	$ 17,801
Revolving Credit Facility
Long term debt and capital lease obligations
Debt	[1]	0		0		135,000
Senior Notes due 2024
Long term debt and capital lease obligations
Debt	[2]	226,709		226,709		245,854
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Debt						53,035
Debt, non-current		50,072		50,072
Revolving Credit Facility
Long term debt and capital lease obligations
Current	[1]	0		0		0
Senior Notes due 2024
Long term debt and capital lease obligations
Current	[2]	0		0		0
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Current						$ 24,937
Debt, current		$ 21,939		$ 21,939
Revolving Credit Facility
Long term debt and capital lease obligations
Stated interest rate		5.60%		5.60%

[1] Unamortized debt issuance costs of $2.5 million and $2.2 million at September 30, 2019 and December 31, 2018, respectively, included in Other Non-Current Assets.

[2] Net of unamortized debt issuance costs of $3.3 million and $4.1 million at September 30, 2019 and December 31, 2018, respectively.