Debt (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Long term debt and capital lease obligations
Current		$ 21,772		$ 21,772		$ 24,937
Debt		348,205		348,205		433,889
Finance Lease, Interest Expense		1,142	$ 515	2,249	$ 1,039
Interest expenses incurred for various debt instruments
Interest paid on Senior Notes due 2024		3,671	3,672	7,344	7,344
Interest paid on Revolving Credit Facility		1,953	1,369	3,806	2,521
Amortization of Debt Issuance Costs		390	324	732	649
Accretion		180	327	359	651
Interest Expense, Debt		2	6	2	114
Capitalized interest		(513)	(195)	(1,213)	(335)
Total interest expense, net of capitalized interest		6,825	$ 6,018	13,279	$ 11,983
Revolving Credit Facility
Long term debt and capital lease obligations
Debt	[1]	53,000		53,000		135,000
Senior Notes due 2024
Long term debt and capital lease obligations
Debt	[2]	246,237		246,237		245,854
Capital Lease Obligations [Member]
Long term debt and capital lease obligations
Debt						53,035
Debt, non-current		48,968		48,968
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		$ 21,772		$ 21,772
Revolving Credit Facility
Long term debt and capital lease obligations
Stated interest rate		5.90%		5.90%

[1] Unamortized debt issuance costs of $2.7 million and $2.2 million at June 30, 2019 and December 31, 2018, respectively, included in Other Non-Current Assets.

[2] Net of unamortized debt issuance costs of $3.8 million and $4.1 million at June 30, 2019 and December 31, 2018, respectively.