Changes in Operations Australia - Arrium (Details) $ in Thousands, AUD in Millions	3 Months Ended		9 Months Ended		12 Months Ended		48 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 AUD	Dec. 31, 2016 USD ($)	Dec. 31, 2015 AUD carload	Dec. 31, 2015 USD ($) carload	Dec. 31, 2014 USD ($)
Operating revenues	$ 482,616	$ 397,030
Australian Operations [Member]
Asset impairment charges	13,000
Write-off of accounts receivable	8,100
Operating revenues	$ 51,798	$ 59,942
Arrium Limited [Member]
Amount invested in capital project							$ 78,000
Annual carloads transported | carload					8,300	8,300
Operating revenues					AUD 83	$ 62,000
Scenario, Forecast [Member] | Middleback Range and Whyalla SteelWorks [Member] | Australian Operations [Member]
Operating revenues			AUD 35	$ 26,000