Offsetting Assets and Liabilties - Offsetting of Liabilties (Details) (USD $)	Mar. 31, 2014	Mar. 31, 2013
Offsetting Liabilities [Line Items]
Gross Amount Of Recognized Liabilties	$ 651,246,000	$ 318,557,000
Gross Amount Of Liabilties Offset In The Balance Sheet	0	0
Net Amount Of Liabilities Presented In The Balance Sheet	651,246,000	318,557,000
Gross Amount Of Financial Instruments Posted Not Offset in Balance Sheet	(650,663,000)	(318,557,000)
Gross Amounts Of Cash Posted Not Offset In Balance Sheet	(583,000)	0
Net Amount Of Liabilities	0	0
Repurchase Agreement [Member]
Offsetting Liabilities [Line Items]
Gross Amount Of Recognized Liabilties	651,246,000	318,557,000
Gross Amount Of Liabilties Offset In The Balance Sheet	0	0
Net Amount Of Liabilities Presented In The Balance Sheet	651,246,000	318,557,000
Gross Amount Of Financial Instruments Posted Not Offset in Balance Sheet	(650,663,000)	(318,557,000)
Gross Amounts Of Cash Posted Not Offset In Balance Sheet	(583,000)	0
Net Amount Of Liabilities	$ 0	$ 0