Allowance for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance at beginning of year	$ 111,215	$ 150,122	$ 179,644
Provision	7,733	33,887	50,325
Charge-offs	(49,353)	(82,562)	(88,886)
Recoveries	10,220	9,768	9,039
Allowance at end of year	79,815	111,215	150,122
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance at beginning of year	85,153	106,445	126,553
Provision	(3,107)	30,869	36,621
Charge-offs	(34,265)	(57,685)	(62,558)
Recoveries	6,800	5,524	5,829
Allowance at end of year	54,581	85,153	106,445
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance at beginning of year	2,467	3,649	2,650
Provision	5,897	1,384	4,002
Charge-offs	(4,946)	(3,259)	(3,302)
Recoveries	219	693	299
Allowance at end of year	3,637	2,467	3,649
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance at beginning of year	13,027	20,487	20,658
Provision	6,414	(2,546)	13,346
Charge-offs	(6,659)	(6,625)	(15,005)
Recoveries	1,743	1,711	1,488
Allowance at end of year	14,525	13,027	20,487
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance at beginning of year	10,568	19,541	29,783
Provision	(1,471)	4,180	(3,644)
Charge-offs	(3,483)	(14,993)	(8,021)
Recoveries	1,458	1,840	1,423
Allowance at end of year	$ 7,072	$ 10,568	$ 19,541