Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Deferred Tax Assets
Inventories	$ 24,202	$ 20,956
Accounts receivable	0	478
Deferred rental income	16,519	15,927
Insurance reserves	13,622	15,029
Litigation settlement and other reserves	3,856	6,229
Asset retirement obligations	6,463	4,960
Stock-based compensation	25,826	28,217
Other	19,694	11,958
Net operating loss carryforwards	16,419	18,358	[1]
Valuation allowance	(2,127)	(2,216)	[1]
Deferred tax assets, net	124,474	119,896
Deferred Tax Liabilities
Accounts receivable	(937)	0
Plant and equipment	(713,132)	(699,487)
Intangible assets	(170,310)	(151,908)
Other	(12,145)	(12,841)
Deferred tax liabilities	(896,524)	(864,236)
Net deferred tax liability	$ (772,050)	$ (744,340)

[1] Prior year amounts have been reclassified to conform to the current presentation.