Comprehensive Income (Schedule of Reclassifications of Recognized Transactions out of AOCI) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains (losses) on available-for-sale securities	$ 2,143	$ 1,071	$ 2,269	$ 539
Taxes	(11,400)	(23,303)	(23,157)	(35,457)
Reclassification of realized transactions, net of taxes	99,806	(21,184)	178,385	57,526
Reclassification out of Accumulated Other Comprehensive Income \| Unrealized gains (losses) on available-for-sale securities
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gains (losses) on available-for-sale securities	2,116	29	2,166	221
Taxes	(776)	0	(776)	(51)
Reclassification of realized transactions, net of taxes	$ 1,340	$ 29	$ 1,390	$ 170

The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to pretax Income or Loss from continuing operations; income tax expense or benefit may include interest and penalties on tax uncertainties based on the entity's accounting policy.

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-Name FASB Interpretation (FIN)

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Statement of Financial Accounting Standard (FAS)

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-Name Accounting Standards Codification

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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Reference 12: http://www.xbrl.org/2003/role/presentationRef

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-Publisher FASB

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-Name Emerging Issues Task Force (EITF)

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+ Details