Components of Working Capital - Accrued Liabilities Table (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Components Of Working Capital [Abstract]
Accrued interest expense		$ 50,031	$ 40,646
Short-term asset retirement obligations		1,339	2,304
Short-term remediation and reclamation obligations		833	833
Income taxes payable		2,666	2,495
Contract liabilities		22,024	0
Other		2,229	1,714
Total accrued liabilities	[1]	$ 79,122	$ 47,992

[1] Accrued liabilities includes affiliate amounts of $2.1 million and $0.2 million as of March 31, 2018, and December 31, 2017, respectively.