Disposals and Impairments - Sale of General Partner Interest (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Disposals and Impairments
Proceeds from sale of general partner interest in TLP		$ 343,135	$ 0	$ 0
Deferred gain on sale of general partner interest in TLP	$ 30,113	30,113	$ 0
General Partner Interest in TLP
Disposals and Impairments
Proceeds from sale of general partner interest in TLP	350,000
Gain on disposal	329,900
Deferred gain on disposal	$ 204,600	204,600
Deferred gain on disposal, amortization period	7 years
Recognized gain	$ 5,000
Future Amortization [Abstract]
2017	30,113	30,113
2018	30,113	30,113
2019	30,113	30,113
2020	30,113	30,113
2021	29,593	29,593
Thereafter	49,487	49,487
Total	199,532	199,532
Accrued expenses and other payables | General Partner Interest in TLP
Disposals and Impairments
Deferred gain on sale of general partner interest in TLP	30,100	30,100
Other Noncurrent Liabilities | General Partner Interest in TLP
Disposals and Impairments
Deferred gain on sale of general partner interest in TLP, Noncurrent	$ 169,400	$ 169,400