Available-For-Sale Securities (Available-For-Sale Securities, Continuous Unrealized Loss Position, Fair Value) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	$ 65,004
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(350)
Continuous unrealized losses existing for greater than 12 months, Fair value	907,945
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(59,191)
Total, Fair value	972,949
Total, Unrealized losses	(59,541)
US Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	10,006
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3)
Continuous unrealized losses existing for greater than 12 months, Fair value	189,172
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(10,981)
Total, Fair value	199,178
Total, Unrealized losses	(10,984)
U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	13,557
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(78)
Continuous unrealized losses existing for greater than 12 months, Fair value	447,369
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(35,291)
Total, Fair value	460,926
Total, Unrealized losses	(35,369)
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	9,029
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(113)
Continuous unrealized losses existing for greater than 12 months, Fair value	47,937
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,768)
Total, Fair value	56,966
Total, Unrealized losses	(1,881)
Corporate Notes, Financial Issuers [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	1,318
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3)
Continuous unrealized losses existing for greater than 12 months, Fair value	57,982
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,205)
Total, Fair value	59,300
Total, Unrealized losses	(1,208)
Corporate Notes, Other [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 Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	14,619
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3)
Continuous unrealized losses existing for greater than 12 months, Fair value	141,358
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(8,935)
Total, Fair value	155,977
Total, Unrealized losses	(8,938)
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	16,475
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(150)
Continuous unrealized losses existing for greater than 12 months, Fair value	13,728
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(613)
Total, Fair value	30,203
Total, Unrealized losses	(763)
Equity 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	10,399
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(398)
Total, Fair value	10,399
Total, Unrealized losses	$ (398)