Investment Securities Gross Unrealized Losses and Fair Values of Investments by Category and Length of Time in a Continuous Unrealized Loss Position (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 1,307,708
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(53,230)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	197,143
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	(24,433)
Estimated Fair Value, Total	1,504,851
Unrealized Losses, Total	(77,663)
US Government-sponsored Enterprises Debt Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	59
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	(1)
Estimated Fair Value, Total	59
Unrealized Losses, Total	(1)
State and Municipal Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	54,679
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(2,698)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	0
Estimated Fair Value, Total	54,679
Unrealized Losses, Total	(2,698)
Corporate Debt Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	6,889
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(108)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	42,989
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	(6,728)
Estimated Fair Value, Total	49,878
Unrealized Losses, Total	(6,836)
Collateralized Mortgage Obligations [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	746,630
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(40,149)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	0
Estimated Fair Value, Total	746,630
Unrealized Losses, Total	(40,149)
Collateralized Mortgage Backed Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	499,406
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(10,271)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	0
Estimated Fair Value, Total	499,406
Unrealized Losses, Total	(10,271)
Auction Rate Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	87
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(3)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	153,245
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	(17,575)
Estimated Fair Value, Total	153,332
Unrealized Losses, Total	(17,578)
Debt Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,307,691
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(53,229)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	196,293
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	(24,304)
Estimated Fair Value, Total	1,503,984
Unrealized Losses, Total	(77,533)
Equity Securities [Member]
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	17
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	(1)
Estimated Fair Value, Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	850
Unrealized Losses, Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses,	(129)
Estimated Fair Value, Total	867
Unrealized Losses, Total	$ (130)