Available-For-Sale Securities (Available-For-Sale Securities, Continuous Unrealized Loss Position, Fair Value) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	$ 917,850
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(69,372)
Continuous unrealized losses existing for greater than 12 months, Fair value	144,947
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(13,766)
Total, Fair value	1,062,797
Total, Unrealized losses	(83,138)
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	185,734
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(14,438)
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	185,734
Total, Unrealized losses	(14,438)
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	413,113
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(37,142)
Continuous unrealized losses existing for greater than 12 months, Fair value	60,240
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(6,432)
Total, Fair value	473,353
Total, Unrealized losses	(43,574)
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	78,209
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3,342)
Continuous unrealized losses existing for greater than 12 months, Fair value	696
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(4)
Total, Fair value	78,905
Total, Unrealized losses	(3,346)
Corporate Notes and Other, Financial Issuers [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	16,530
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(232)
Continuous unrealized losses existing for greater than 12 months, Fair value	63,661
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(2,281)
Total, Fair value	80,191
Total, Unrealized losses	(2,513)
Corporate Notes and Other, Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	985
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(15)
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	985
Total, Unrealized losses	(15)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	175,261
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(12,861)
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	175,261
Total, Unrealized losses	(12,861)
Mortgage-Backed, Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	33,511
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(728)
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	33,511
Total, Unrealized losses	(728)
Other Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	14,507
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(614)
Continuous unrealized losses existing for greater than 12 months, Fair value	20,350
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(5,049)
Total, Fair value	34,857
Total, Unrealized losses	$ (5,663)