Income Taxes - Significant Components of Net Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Components of Deferred Tax Assets and Liabilities [Abstract]
Basis differences in equipment	$ (31,255)	$ (29,107)
Basis differences in intangible assets	(287)	2,479
Net operating losses	6,841	5,672
Accounts receivable	1,673	1,671
State income taxes	992	623
Accruals not currently deductible for income tax purposes	7,913	8,057
Basis differences associated with acquired investments	(21,612)	(14,308)
Other	5,622	4,907
Total deferred taxes	(30,113)	(20,006)
Net deferred taxes	(30,113)	(20,006)
Current deferred tax asset	6,496	16,834
Noncurrent deferred tax liability	$ (36,609)	$ (36,840)