Changes in Operations Australia GRail (Details) AUD in Thousands, $ in Thousands, carload in Millions			3 Months Ended			12 Months Ended
	Dec. 01, 2016 AUD wagon locomotive Train_Sets	Dec. 01, 2016 USD ($)	Mar. 31, 2017 AUD	Mar. 31, 2017 USD ($)	Dec. 31, 2016 AUD	Dec. 31, 2017 AUD carload	Dec. 31, 2016 AUD	Dec. 31, 2016 USD ($) $ / AUD	Dec. 31, 2017 USD ($)	May 03, 2017 USD ($) $ / AUD	Dec. 01, 2016 USD ($) wagon locomotive Train_Sets	Dec. 31, 2015 $ / AUD	Dec. 31, 2015 $ / £	Mar. 25, 2015 $ / £
Foreign Currency Exchange Rate, Translation								0.74		1.29		0.75	1.51	1.49
Noncontrolling Interest, Ownership Percentage by Parent						51.10%			51.10%
Debt Issuance Costs, Gross | $								$ 42,495	$ 43,950
GOODWILL | $								1,125,596	$ 1,165,587
Credit Agreement [Member] | Australian Term Loan [Member]
Repayments of Debt					AUD 250,000		AUD 250,000	$ 185,300
Australia Credit Agreement
Debt Instrument, Term					5 years
Proceeds from Issuance of Debt					AUD 690,000
MIRA [Member]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners						48.90%			48.90%
GRail [Member]
Business Acquisition, Effective Date of Acquisition	Dec. 01, 2016	Dec. 01, 2016
Cash consideration	AUD 1,140,000	$ 844,900
Percentage Consolidated	100.00%	100.00%
Business Combination, Consideration Transferred	AUD 1,300,000
Business Combination, Acquisition Related Costs						AUD 13,200
Debt Issuance Costs, Gross						AUD 19,800
Business Combination, Rail Haulage Contract, Term of Contract	20 years	20 years
Business Combination, Rail Haulage Contract, Period of Minimum Guaranteed Volumes	18 years	18 years
Entity Number of Train Sets Owned or Leased | Train_Sets	9										9
Entity Number of Locomotives Owned or Leased | locomotive	30										30
Entity Number of Wagons Owned or Leased | wagon	894										894
Proceeds from Previous Acquisition			AUD 3,800	$ 2,900
Accounts receivable	AUD 1,556										$ 1,153
Materials and supplies	411										305
Property and equipment	279,592										207,206
GOODWILL	415,959										308,267
Total assets	1,332,518										987,530
Accounts payable and accrued expenses	5,796										4,296
Deferred income tax liabilities, net	190,551										141,217
Net assets	1,136,171										$ 842,017
Goodwill deductible for tax purposes | $										$ 0
GRail [Member] | Customer Contracts [Member]
Intangible assets	AUD 635,000	$ 470,599
GRail [Member] | Steam Coal [Domain]
Annual Tonnes Hauled | carload						40