Consolidated Statements of Changes in Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Less: Treasury Common Stock	Less: Treasury Preferred Stock	Less: Unearned Employee Stock Ownership Plan Shares
Balance at Mar. 31, 2011	$ 993,020	$ 10,497	$ 425,212	$ (46,467)	$ 1,140,002	$ (525,653)	$ (7,189)	$ (3,382)
Consolidated statement of change in equity
Increase in market value of released ESOP shares	3,141		3,141
Release of unearned ESOP Shares	984							984
Foreign currency translation	(2,854)			(2,854)
Unrealized gain on investments, net of tax	10,005			10,005
Fair market value of cash flow hedges, net of tax	(5,691)			(5,691)
Adjustment to postretirement benefit obligation	(429)			(429)
Net earnings	205,367				205,367
Less: Excess of redemption value over carrying value of preferred shares redeemed	(5,908)				(5,908)
Preferred stock dividends paid	(2,913)				(2,913)
Common stock dividends	(19,484)				(19,484)
Redemption of preferred shares	(144,808)						(144,808)
Contribution from related party	5,390		5,390
Net activity	42,800		8,531	1,031	177,062		(144,808)	984
Balance at Mar. 31, 2012	1,035,820	10,497	433,743	(45,436)	1,317,064	(525,653)	(151,997)	(2,398)
Consolidated statement of change in equity
Adjustment to initially apply ASU 2010-26	(1,721)				(1,721)
Increase in market value of released ESOP shares	4,425		4,425
Release of unearned ESOP Shares	692							692
Foreign currency translation	(1,271)			(1,271)
Unrealized gain on investments, net of tax	18,779			18,779
Fair market value of cash flow hedges, net of tax	5,831			5,831
Adjustment to postretirement benefit obligation	(583)			(583)
Net earnings	264,708				264,708
Less: Excess of redemption value over carrying value of preferred shares redeemed
Preferred stock dividends paid
Common stock dividends	(97,421)				(97,421)
Net activity	193,439		4,425	22,756	165,566			692
Balance at Mar. 31, 2013	1,229,259	10,497	438,168	(22,680)	1,482,630	(525,653)	(151,997)	(1,706)
Consolidated statement of change in equity
Increase in market value of released ESOP shares	6,042		6,042
Release of unearned ESOP Shares	487							487
Foreign currency translation	(9,134)			(9,134)
Unrealized gain on investments, net of tax	(33,654)			(33,654)
Fair market value of cash flow hedges, net of tax	11,977			11,977
Adjustment to postretirement benefit obligation	(432)			(432)
Net earnings	342,391				342,391
Less: Excess of redemption value over carrying value of preferred shares redeemed
Preferred stock dividends paid
Common stock dividends	(19,568)				(19,568)
Net activity	298,109		6,042	(31,243)	322,823			487
Balance at Mar. 31, 2014	$ 1,527,368	$ 10,497	$ 444,210	$ (53,923)	$ 1,805,453	$ (525,653)	$ (151,997)	$ (1,219)