Income Taxes (Components of Income Tax Expense) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended						12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013		Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Current [Abstract]
Federal							$ 184,308	$ 145,603	$ 94,665
Foreign							4,561	7,042	2,758
State							19,121	13,589	12,817
Total current income tax expense							207,990	166,234	110,240
Deferred [Abstract]
Federal							(4,722)	26,993	65,456
Foreign							(1,127)	(975)	474
State							(1,020)	10,291	2,622
Total deferred income tax expense							(6,869)	36,309	68,552
Income tax expense	$ (1,800)	$ 0	[1]	$ (1,493)	$ 0	[1]	$ 201,121	$ 202,543	$ 178,792

[1] During the three months ended September 30, 2013, the Company recognized a $1.5 million tax benefit related to a change in a state income tax law, allowing the Company to utilize additional net operating loss carryforwards. During the three months ended March 31, 2014, the Company recognized an additional $1.8 million