Investment Securities Gross Unrealized Losses and Fair Values of Investments by Category and Length of Time in a Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2016 USD ($)
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 226,700
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,160)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	397,554
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(17,091)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	624,254
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(18,251)
State and Municipal Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	91,790
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(735)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	91,790
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(735)
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	4,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(35)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	33,766
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5,315)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	37,766
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(5,350)
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	124,739
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(376)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	266,062
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2,395)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	390,801
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2,771)
Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	6,171
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(14)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	6,171
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(14)
Auction Rate Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	97,726
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(9,381)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	97,726
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(9,381)
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	226,700
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,160)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	397,554
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(17,091)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	624,254
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(18,251)
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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