Available-For-Sale Securities (Schedule Of Available-For-Sale Securities Portfolio Continuous Unrealized Loss Position) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	$ 910,054
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(11,019)
Continuous unrealized losses existing for greater than 12 months, Fair value	104,570
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(3,268)
Total, Fair value	1,014,624
Total, Unrealized losses	(14,287)
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	197,422
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(2,760)
Continuous unrealized losses existing for greater than 12 months, Fair value	0
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	0
Total, Fair value	197,422
Total, Unrealized losses	(2,760)
U.S. Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	510,371
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(4,629)
Continuous unrealized losses existing for greater than 12 months, Fair value	6,032
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(2)
Total, Fair value	516,403
Total, Unrealized losses	(4,631)
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	19,977
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(314)
Continuous unrealized losses existing for greater than 12 months, Fair value	463
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(2)
Total, Fair value	20,440
Total, Unrealized losses	(316)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	4,606
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(37)
Continuous unrealized losses existing for greater than 12 months, Fair value	73,696
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(2,243)
Total, Fair value	78,302
Total, Unrealized losses	(2,280)
Corporate Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	0
Continuous unrealized losses existing for less than 12 months, Unrealized losses	0
Continuous unrealized losses existing for greater than 12 months, Fair value	0
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	0
Total, Fair value	0
Total, Unrealized losses	0
Mortgage Backed Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	158,142
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3,194)
Continuous unrealized losses existing for greater than 12 months, Fair value	0
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	0
Total, Fair value	158,142
Total, Unrealized losses	(3,194)
Mortgage-Backed, Non-Agency CMOs [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	13,616
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(5)
Continuous unrealized losses existing for greater than 12 months, Fair value	0
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	0
Total, Fair value	13,616
Total, Unrealized losses	(5)
Other equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	5,920
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(80)
Continuous unrealized losses existing for greater than 12 months, Fair value	24,379
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,021)
Total, Fair value	30,299
Total, Unrealized losses	$ (1,101)