Income Taxes (Details 3) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Non-cash share-based payments	$ 1,899	$ 2,183	$ 1,483
Net operating loss carry forwards	22,804	47,538	52,007
Other	1,272	1,902	761
Total deferred tax assets	25,975	51,623	54,251
Deferred tax liabilities:
Accelerated depreciation	(62,379)	(92,734)	(87,716)
Other	354	(1,227)	(442)
Total deferred tax liabilities	62,025	93,961	88,158
Deferred Income Tax Liabilities, Net	(36,050)	(42,338)	$ (33,907)
Deferred Tax Liabilities, Net	$ (36,547)	$ (44,241)